| Message ID | ed493525-57c8-6a2c-6be0-bd6b36562f09@kernel.dk (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Delegated to: | Mike Snitzer |
| Headers | show |
On Mon, Sep 11 2017 at 5:27pm -0400, Jens Axboe <axboe@kernel.dk> wrote: > On 09/11/2017 03:13 PM, Mike Snitzer wrote: > > On Mon, Sep 11 2017 at 4:51pm -0400, > > Jens Axboe <axboe@kernel.dk> wrote: > > > >> On 09/11/2017 10:16 AM, Mike Snitzer wrote: > >>> Here is v2 that should obviate the need to rename blk_mq_insert_request > >>> (by using bools to control run_queue and async). > >>> > >>> As for inserting directly into dispatch, if that can be done that is > >>> great but I'd prefer to have that be a follow-up optimization. This > >>> fixes the regression in question, and does so in well-known terms. > >>> > >>> What do you think? > >> > >> I think it looks reasonable. My only concern is the use of the software > >> queues. Depending on the scheduler, they may or may not be used. I'd > >> need to review the code, but my first thought is that this would break > >> if you use blk_mq_insert_request() on a device that is managed by > >> mq-deadline or bfq, for instance. Schedulers are free to use the > >> software queues, but they are also free to ignore them and use internal > >> queuing. > >> > >> Looking at the code, looks like this was changed slightly at some point, > >> we always flush the software queues, if any of them contain requests. So > >> it's probably fine. > > > > OK good, but is that too brittle to rely on? Something that might change > > in the future? > > I'm actually surprised we do flush software queues for that case, since > we don't always have to. So it is a bit of a wart. If we don't have a > scheduler, software queues is where IO goes. If we have a scheduler, the > scheduler has complete control of where to queue IO. Generally, the > scheduler will either utilize the software queues or it won't, there's > nothing in between. > > I know realize I'm an idiot and didn't read it right. So here's the code > in question: > > const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request; > > [...] > > } else if (!has_sched_dispatch) { > blk_mq_flush_busy_ctxs(hctx, &rq_list); > blk_mq_dispatch_rq_list(q, &rq_list); > } > > so we do only enter sw queue flushing, if we don't have a scheduler with > a dispatch_request hook. So now I am really wondering how your patch > could work if the bottom device has bfq or mq-deadline attached? I didn't test it.. I was an even bigger idiot and assumed blk-mq core wouldn't alter its IO processing based on scheduler or no. Nevermind that I tagged my patch for stable@ without testing.. /me knows better > >> My earlier suggestion to use just hctx->dispatch for the IO and bypass > >> the software queues completely. The use case for the dispatch list is > >> the same, regardless of whether the device has a scheduler attached or > >> not. > > > > I'm missing how these details relate to the goal of bypassing any > > scheduler that might be attached. Are you saying the attached elevator > > would still get in the way? > > See above. Yeap, got it. > > Looking at blk_mq_sched_insert_request(), submission when an elevator > > isn't attached is exactly what I made blk_mq_insert_request() do > > (which is exactly what it did in the past). > > Right, but that path is only used if we don't have a scheduler attached. > So while the code will use that path IFF a scheduler isn't attached to > that device, your use case will use it for both cases. > > > In the case of DM multipath, nothing else should be submitting IO to > > the device so elevator shouldn't be used -- only interface for > > submitting IO would be blk_mq_insert_request(). So even if a > > scheduler is attached it should be bypassed right? > > The problem is the usage of the sw queue. > > Does the below work for you? I _will_ test your patch and let you know! Thanks, much appreciated. Mike -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
On Mon, Sep 11 2017 at 5:51pm -0400, Mike Snitzer <snitzer@redhat.com> wrote: > On Mon, Sep 11 2017 at 5:27pm -0400, > Jens Axboe <axboe@kernel.dk> wrote: > > > > Does the below work for you? > > I _will_ test your patch and let you know! Tested with bfq on underlying paths and both none and bfq on upper-level DM multipath request_queue. Works perfectly, feel free to add my: Tested-by: Mike Snitzer <snitzer@redhat.com> Thanks again! -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
On 09/11/2017 04:30 PM, Mike Snitzer wrote: > On Mon, Sep 11 2017 at 5:51pm -0400, > Mike Snitzer <snitzer@redhat.com> wrote: > >> On Mon, Sep 11 2017 at 5:27pm -0400, >> Jens Axboe <axboe@kernel.dk> wrote: >>> >>> Does the below work for you? >> >> I _will_ test your patch and let you know! > > Tested with bfq on underlying paths and both none and bfq on upper-level > DM multipath request_queue. > > Works perfectly, feel free to add my: > > Tested-by: Mike Snitzer <snitzer@redhat.com> > > Thanks again! Great, thanks for testing! I'll commit this, stealing your change log almost verbatim.
On Tue, Sep 12, 2017 at 5:27 AM, Jens Axboe <axboe@kernel.dk> wrote: > On 09/11/2017 03:13 PM, Mike Snitzer wrote: >> On Mon, Sep 11 2017 at 4:51pm -0400, >> Jens Axboe <axboe@kernel.dk> wrote: >> >>> On 09/11/2017 10:16 AM, Mike Snitzer wrote: >>>> Here is v2 that should obviate the need to rename blk_mq_insert_request >>>> (by using bools to control run_queue and async). >>>> >>>> As for inserting directly into dispatch, if that can be done that is >>>> great but I'd prefer to have that be a follow-up optimization. This >>>> fixes the regression in question, and does so in well-known terms. >>>> >>>> What do you think? >>> >>> I think it looks reasonable. My only concern is the use of the software >>> queues. Depending on the scheduler, they may or may not be used. I'd >>> need to review the code, but my first thought is that this would break >>> if you use blk_mq_insert_request() on a device that is managed by >>> mq-deadline or bfq, for instance. Schedulers are free to use the >>> software queues, but they are also free to ignore them and use internal >>> queuing. >>> >>> Looking at the code, looks like this was changed slightly at some point, >>> we always flush the software queues, if any of them contain requests. So >>> it's probably fine. >> >> OK good, but is that too brittle to rely on? Something that might change >> in the future? > > I'm actually surprised we do flush software queues for that case, since > we don't always have to. So it is a bit of a wart. If we don't have a > scheduler, software queues is where IO goes. If we have a scheduler, the > scheduler has complete control of where to queue IO. Generally, the > scheduler will either utilize the software queues or it won't, there's > nothing in between. > > I know realize I'm an idiot and didn't read it right. So here's the code > in question: > > const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request; > > [...] > > } else if (!has_sched_dispatch) { > blk_mq_flush_busy_ctxs(hctx, &rq_list); > blk_mq_dispatch_rq_list(q, &rq_list); > } > > so we do only enter sw queue flushing, if we don't have a scheduler with > a dispatch_request hook. So now I am really wondering how your patch > could work if the bottom device has bfq or mq-deadline attached? > >>> My earlier suggestion to use just hctx->dispatch for the IO and bypass >>> the software queues completely. The use case for the dispatch list is >>> the same, regardless of whether the device has a scheduler attached or >>> not. >> >> I'm missing how these details relate to the goal of bypassing any >> scheduler that might be attached. Are you saying the attached elevator >> would still get in the way? > > See above. > >> Looking at blk_mq_sched_insert_request(), submission when an elevator >> isn't attached is exactly what I made blk_mq_insert_request() do >> (which is exactly what it did in the past). > > Right, but that path is only used if we don't have a scheduler attached. > So while the code will use that path IFF a scheduler isn't attached to > that device, your use case will use it for both cases. > >> In the case of DM multipath, nothing else should be submitting IO to >> the device so elevator shouldn't be used -- only interface for >> submitting IO would be blk_mq_insert_request(). So even if a >> scheduler is attached it should be bypassed right? > > The problem is the usage of the sw queue. > > Does the below work for you? > > > diff --git a/block/blk-core.c b/block/blk-core.c > index d709c0e3a2ac..aebe676225e6 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -2342,7 +2342,12 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request * > if (q->mq_ops) { > if (blk_queue_io_stat(q)) > blk_account_io_start(rq, true); > - blk_mq_sched_insert_request(rq, false, true, false, false); > + /* > + * Since we have a scheduler attached on the top device, > + * bypass a potential scheduler on the bottom device for > + * insert. > + */ > + blk_mq_request_bypass_insert(rq); > return BLK_STS_OK; > } > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 3f18cff80050..98a18609755e 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1401,6 +1401,22 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, > blk_mq_hctx_mark_pending(hctx, ctx); > } > > +/* > + * Should only be used carefully, when the caller knows we want to > + * bypass a potential IO scheduler on the target device. > + */ > +void blk_mq_request_bypass_insert(struct request *rq) > +{ > + struct blk_mq_ctx *ctx = rq->mq_ctx; > + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu); > + > + spin_lock(&hctx->lock); > + list_add_tail(&rq->queuelist, &hctx->dispatch); > + spin_unlock(&hctx->lock); > + > + blk_mq_run_hw_queue(hctx, false); > +} > + Hello Jens and Mike, This patch sends flush request to ->dispatch directly too, which changes the previous behaviour, is that OK for dm-rq?
On 09/14/2017 09:57 AM, Ming Lei wrote: > On Tue, Sep 12, 2017 at 5:27 AM, Jens Axboe <axboe@kernel.dk> wrote: >> On 09/11/2017 03:13 PM, Mike Snitzer wrote: >>> On Mon, Sep 11 2017 at 4:51pm -0400, >>> Jens Axboe <axboe@kernel.dk> wrote: >>> >>>> On 09/11/2017 10:16 AM, Mike Snitzer wrote: >>>>> Here is v2 that should obviate the need to rename blk_mq_insert_request >>>>> (by using bools to control run_queue and async). >>>>> >>>>> As for inserting directly into dispatch, if that can be done that is >>>>> great but I'd prefer to have that be a follow-up optimization. This >>>>> fixes the regression in question, and does so in well-known terms. >>>>> >>>>> What do you think? >>>> >>>> I think it looks reasonable. My only concern is the use of the software >>>> queues. Depending on the scheduler, they may or may not be used. I'd >>>> need to review the code, but my first thought is that this would break >>>> if you use blk_mq_insert_request() on a device that is managed by >>>> mq-deadline or bfq, for instance. Schedulers are free to use the >>>> software queues, but they are also free to ignore them and use internal >>>> queuing. >>>> >>>> Looking at the code, looks like this was changed slightly at some point, >>>> we always flush the software queues, if any of them contain requests. So >>>> it's probably fine. >>> >>> OK good, but is that too brittle to rely on? Something that might change >>> in the future? >> >> I'm actually surprised we do flush software queues for that case, since >> we don't always have to. So it is a bit of a wart. If we don't have a >> scheduler, software queues is where IO goes. If we have a scheduler, the >> scheduler has complete control of where to queue IO. Generally, the >> scheduler will either utilize the software queues or it won't, there's >> nothing in between. >> >> I know realize I'm an idiot and didn't read it right. So here's the code >> in question: >> >> const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request; >> >> [...] >> >> } else if (!has_sched_dispatch) { >> blk_mq_flush_busy_ctxs(hctx, &rq_list); >> blk_mq_dispatch_rq_list(q, &rq_list); >> } >> >> so we do only enter sw queue flushing, if we don't have a scheduler with >> a dispatch_request hook. So now I am really wondering how your patch >> could work if the bottom device has bfq or mq-deadline attached? >> >>>> My earlier suggestion to use just hctx->dispatch for the IO and bypass >>>> the software queues completely. The use case for the dispatch list is >>>> the same, regardless of whether the device has a scheduler attached or >>>> not. >>> >>> I'm missing how these details relate to the goal of bypassing any >>> scheduler that might be attached. Are you saying the attached elevator >>> would still get in the way? >> >> See above. >> >>> Looking at blk_mq_sched_insert_request(), submission when an elevator >>> isn't attached is exactly what I made blk_mq_insert_request() do >>> (which is exactly what it did in the past). >> >> Right, but that path is only used if we don't have a scheduler attached. >> So while the code will use that path IFF a scheduler isn't attached to >> that device, your use case will use it for both cases. >> >>> In the case of DM multipath, nothing else should be submitting IO to >>> the device so elevator shouldn't be used -- only interface for >>> submitting IO would be blk_mq_insert_request(). So even if a >>> scheduler is attached it should be bypassed right? >> >> The problem is the usage of the sw queue. >> >> Does the below work for you? >> >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index d709c0e3a2ac..aebe676225e6 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -2342,7 +2342,12 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request * >> if (q->mq_ops) { >> if (blk_queue_io_stat(q)) >> blk_account_io_start(rq, true); >> - blk_mq_sched_insert_request(rq, false, true, false, false); >> + /* >> + * Since we have a scheduler attached on the top device, >> + * bypass a potential scheduler on the bottom device for >> + * insert. >> + */ >> + blk_mq_request_bypass_insert(rq); >> return BLK_STS_OK; >> } >> >> diff --git a/block/blk-mq.c b/block/blk-mq.c >> index 3f18cff80050..98a18609755e 100644 >> --- a/block/blk-mq.c >> +++ b/block/blk-mq.c >> @@ -1401,6 +1401,22 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >> blk_mq_hctx_mark_pending(hctx, ctx); >> } >> >> +/* >> + * Should only be used carefully, when the caller knows we want to >> + * bypass a potential IO scheduler on the target device. >> + */ >> +void blk_mq_request_bypass_insert(struct request *rq) >> +{ >> + struct blk_mq_ctx *ctx = rq->mq_ctx; >> + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu); >> + >> + spin_lock(&hctx->lock); >> + list_add_tail(&rq->queuelist, &hctx->dispatch); >> + spin_unlock(&hctx->lock); >> + >> + blk_mq_run_hw_queue(hctx, false); >> +} >> + > > Hello Jens and Mike, > > This patch sends flush request to ->dispatch directly too, which changes the > previous behaviour, is that OK for dm-rq? That's a good question, I need to look into that. The flush behavior is so annoying. Did you make any progress on fixing up the patch you posted the other day on treating flushes like any other request?
On Fri, Sep 15, 2017 at 12:30 AM, Jens Axboe <axboe@kernel.dk> wrote: > On 09/14/2017 09:57 AM, Ming Lei wrote: >> On Tue, Sep 12, 2017 at 5:27 AM, Jens Axboe <axboe@kernel.dk> wrote: >>> On 09/11/2017 03:13 PM, Mike Snitzer wrote: >>>> On Mon, Sep 11 2017 at 4:51pm -0400, >>>> Jens Axboe <axboe@kernel.dk> wrote: >>>> >>>>> On 09/11/2017 10:16 AM, Mike Snitzer wrote: >>>>>> Here is v2 that should obviate the need to rename blk_mq_insert_request >>>>>> (by using bools to control run_queue and async). >>>>>> >>>>>> As for inserting directly into dispatch, if that can be done that is >>>>>> great but I'd prefer to have that be a follow-up optimization. This >>>>>> fixes the regression in question, and does so in well-known terms. >>>>>> >>>>>> What do you think? >>>>> >>>>> I think it looks reasonable. My only concern is the use of the software >>>>> queues. Depending on the scheduler, they may or may not be used. I'd >>>>> need to review the code, but my first thought is that this would break >>>>> if you use blk_mq_insert_request() on a device that is managed by >>>>> mq-deadline or bfq, for instance. Schedulers are free to use the >>>>> software queues, but they are also free to ignore them and use internal >>>>> queuing. >>>>> >>>>> Looking at the code, looks like this was changed slightly at some point, >>>>> we always flush the software queues, if any of them contain requests. So >>>>> it's probably fine. >>>> >>>> OK good, but is that too brittle to rely on? Something that might change >>>> in the future? >>> >>> I'm actually surprised we do flush software queues for that case, since >>> we don't always have to. So it is a bit of a wart. If we don't have a >>> scheduler, software queues is where IO goes. If we have a scheduler, the >>> scheduler has complete control of where to queue IO. Generally, the >>> scheduler will either utilize the software queues or it won't, there's >>> nothing in between. >>> >>> I know realize I'm an idiot and didn't read it right. So here's the code >>> in question: >>> >>> const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request; >>> >>> [...] >>> >>> } else if (!has_sched_dispatch) { >>> blk_mq_flush_busy_ctxs(hctx, &rq_list); >>> blk_mq_dispatch_rq_list(q, &rq_list); >>> } >>> >>> so we do only enter sw queue flushing, if we don't have a scheduler with >>> a dispatch_request hook. So now I am really wondering how your patch >>> could work if the bottom device has bfq or mq-deadline attached? >>> >>>>> My earlier suggestion to use just hctx->dispatch for the IO and bypass >>>>> the software queues completely. The use case for the dispatch list is >>>>> the same, regardless of whether the device has a scheduler attached or >>>>> not. >>>> >>>> I'm missing how these details relate to the goal of bypassing any >>>> scheduler that might be attached. Are you saying the attached elevator >>>> would still get in the way? >>> >>> See above. >>> >>>> Looking at blk_mq_sched_insert_request(), submission when an elevator >>>> isn't attached is exactly what I made blk_mq_insert_request() do >>>> (which is exactly what it did in the past). >>> >>> Right, but that path is only used if we don't have a scheduler attached. >>> So while the code will use that path IFF a scheduler isn't attached to >>> that device, your use case will use it for both cases. >>> >>>> In the case of DM multipath, nothing else should be submitting IO to >>>> the device so elevator shouldn't be used -- only interface for >>>> submitting IO would be blk_mq_insert_request(). So even if a >>>> scheduler is attached it should be bypassed right? >>> >>> The problem is the usage of the sw queue. >>> >>> Does the below work for you? >>> >>> >>> diff --git a/block/blk-core.c b/block/blk-core.c >>> index d709c0e3a2ac..aebe676225e6 100644 >>> --- a/block/blk-core.c >>> +++ b/block/blk-core.c >>> @@ -2342,7 +2342,12 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request * >>> if (q->mq_ops) { >>> if (blk_queue_io_stat(q)) >>> blk_account_io_start(rq, true); >>> - blk_mq_sched_insert_request(rq, false, true, false, false); >>> + /* >>> + * Since we have a scheduler attached on the top device, >>> + * bypass a potential scheduler on the bottom device for >>> + * insert. >>> + */ >>> + blk_mq_request_bypass_insert(rq); >>> return BLK_STS_OK; >>> } >>> >>> diff --git a/block/blk-mq.c b/block/blk-mq.c >>> index 3f18cff80050..98a18609755e 100644 >>> --- a/block/blk-mq.c >>> +++ b/block/blk-mq.c >>> @@ -1401,6 +1401,22 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >>> blk_mq_hctx_mark_pending(hctx, ctx); >>> } >>> >>> +/* >>> + * Should only be used carefully, when the caller knows we want to >>> + * bypass a potential IO scheduler on the target device. >>> + */ >>> +void blk_mq_request_bypass_insert(struct request *rq) >>> +{ >>> + struct blk_mq_ctx *ctx = rq->mq_ctx; >>> + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu); >>> + >>> + spin_lock(&hctx->lock); >>> + list_add_tail(&rq->queuelist, &hctx->dispatch); >>> + spin_unlock(&hctx->lock); >>> + >>> + blk_mq_run_hw_queue(hctx, false); >>> +} >>> + >> >> Hello Jens and Mike, >> >> This patch sends flush request to ->dispatch directly too, which changes the >> previous behaviour, is that OK for dm-rq? > > That's a good question, I need to look into that. The flush behavior is so > annoying. Did you make any progress on fixing up the patch you posted the > other day on treating flushes like any other request? It has been ready, will post it out later.
On 09/14/2017 10:33 AM, Ming Lei wrote: > On Fri, Sep 15, 2017 at 12:30 AM, Jens Axboe <axboe@kernel.dk> wrote: >> On 09/14/2017 09:57 AM, Ming Lei wrote: >>> On Tue, Sep 12, 2017 at 5:27 AM, Jens Axboe <axboe@kernel.dk> wrote: >>>> On 09/11/2017 03:13 PM, Mike Snitzer wrote: >>>>> On Mon, Sep 11 2017 at 4:51pm -0400, >>>>> Jens Axboe <axboe@kernel.dk> wrote: >>>>> >>>>>> On 09/11/2017 10:16 AM, Mike Snitzer wrote: >>>>>>> Here is v2 that should obviate the need to rename blk_mq_insert_request >>>>>>> (by using bools to control run_queue and async). >>>>>>> >>>>>>> As for inserting directly into dispatch, if that can be done that is >>>>>>> great but I'd prefer to have that be a follow-up optimization. This >>>>>>> fixes the regression in question, and does so in well-known terms. >>>>>>> >>>>>>> What do you think? >>>>>> >>>>>> I think it looks reasonable. My only concern is the use of the software >>>>>> queues. Depending on the scheduler, they may or may not be used. I'd >>>>>> need to review the code, but my first thought is that this would break >>>>>> if you use blk_mq_insert_request() on a device that is managed by >>>>>> mq-deadline or bfq, for instance. Schedulers are free to use the >>>>>> software queues, but they are also free to ignore them and use internal >>>>>> queuing. >>>>>> >>>>>> Looking at the code, looks like this was changed slightly at some point, >>>>>> we always flush the software queues, if any of them contain requests. So >>>>>> it's probably fine. >>>>> >>>>> OK good, but is that too brittle to rely on? Something that might change >>>>> in the future? >>>> >>>> I'm actually surprised we do flush software queues for that case, since >>>> we don't always have to. So it is a bit of a wart. If we don't have a >>>> scheduler, software queues is where IO goes. If we have a scheduler, the >>>> scheduler has complete control of where to queue IO. Generally, the >>>> scheduler will either utilize the software queues or it won't, there's >>>> nothing in between. >>>> >>>> I know realize I'm an idiot and didn't read it right. So here's the code >>>> in question: >>>> >>>> const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request; >>>> >>>> [...] >>>> >>>> } else if (!has_sched_dispatch) { >>>> blk_mq_flush_busy_ctxs(hctx, &rq_list); >>>> blk_mq_dispatch_rq_list(q, &rq_list); >>>> } >>>> >>>> so we do only enter sw queue flushing, if we don't have a scheduler with >>>> a dispatch_request hook. So now I am really wondering how your patch >>>> could work if the bottom device has bfq or mq-deadline attached? >>>> >>>>>> My earlier suggestion to use just hctx->dispatch for the IO and bypass >>>>>> the software queues completely. The use case for the dispatch list is >>>>>> the same, regardless of whether the device has a scheduler attached or >>>>>> not. >>>>> >>>>> I'm missing how these details relate to the goal of bypassing any >>>>> scheduler that might be attached. Are you saying the attached elevator >>>>> would still get in the way? >>>> >>>> See above. >>>> >>>>> Looking at blk_mq_sched_insert_request(), submission when an elevator >>>>> isn't attached is exactly what I made blk_mq_insert_request() do >>>>> (which is exactly what it did in the past). >>>> >>>> Right, but that path is only used if we don't have a scheduler attached. >>>> So while the code will use that path IFF a scheduler isn't attached to >>>> that device, your use case will use it for both cases. >>>> >>>>> In the case of DM multipath, nothing else should be submitting IO to >>>>> the device so elevator shouldn't be used -- only interface for >>>>> submitting IO would be blk_mq_insert_request(). So even if a >>>>> scheduler is attached it should be bypassed right? >>>> >>>> The problem is the usage of the sw queue. >>>> >>>> Does the below work for you? >>>> >>>> >>>> diff --git a/block/blk-core.c b/block/blk-core.c >>>> index d709c0e3a2ac..aebe676225e6 100644 >>>> --- a/block/blk-core.c >>>> +++ b/block/blk-core.c >>>> @@ -2342,7 +2342,12 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request * >>>> if (q->mq_ops) { >>>> if (blk_queue_io_stat(q)) >>>> blk_account_io_start(rq, true); >>>> - blk_mq_sched_insert_request(rq, false, true, false, false); >>>> + /* >>>> + * Since we have a scheduler attached on the top device, >>>> + * bypass a potential scheduler on the bottom device for >>>> + * insert. >>>> + */ >>>> + blk_mq_request_bypass_insert(rq); >>>> return BLK_STS_OK; >>>> } >>>> >>>> diff --git a/block/blk-mq.c b/block/blk-mq.c >>>> index 3f18cff80050..98a18609755e 100644 >>>> --- a/block/blk-mq.c >>>> +++ b/block/blk-mq.c >>>> @@ -1401,6 +1401,22 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >>>> blk_mq_hctx_mark_pending(hctx, ctx); >>>> } >>>> >>>> +/* >>>> + * Should only be used carefully, when the caller knows we want to >>>> + * bypass a potential IO scheduler on the target device. >>>> + */ >>>> +void blk_mq_request_bypass_insert(struct request *rq) >>>> +{ >>>> + struct blk_mq_ctx *ctx = rq->mq_ctx; >>>> + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu); >>>> + >>>> + spin_lock(&hctx->lock); >>>> + list_add_tail(&rq->queuelist, &hctx->dispatch); >>>> + spin_unlock(&hctx->lock); >>>> + >>>> + blk_mq_run_hw_queue(hctx, false); >>>> +} >>>> + >>> >>> Hello Jens and Mike, >>> >>> This patch sends flush request to ->dispatch directly too, which changes the >>> previous behaviour, is that OK for dm-rq? >> >> That's a good question, I need to look into that. The flush behavior is so >> annoying. Did you make any progress on fixing up the patch you posted the >> other day on treating flushes like any other request? > > It has been ready, will post it out later. OK good, if that's clean enough, then I think going that route is a much better idea than introducing more flush/not-flush logic. I liked the initial patch from a concept point of view, and it enables us to get rid of a few nasty hacks.
diff --git a/block/blk-core.c b/block/blk-core.c index d709c0e3a2ac..aebe676225e6 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -2342,7 +2342,12 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request * if (q->mq_ops) { if (blk_queue_io_stat(q)) blk_account_io_start(rq, true); - blk_mq_sched_insert_request(rq, false, true, false, false); + /* + * Since we have a scheduler attached on the top device, + * bypass a potential scheduler on the bottom device for + * insert. + */ + blk_mq_request_bypass_insert(rq); return BLK_STS_OK; } diff --git a/block/blk-mq.c b/block/blk-mq.c index 3f18cff80050..98a18609755e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1401,6 +1401,22 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, blk_mq_hctx_mark_pending(hctx, ctx); } +/* + * Should only be used carefully, when the caller knows we want to + * bypass a potential IO scheduler on the target device. + */ +void blk_mq_request_bypass_insert(struct request *rq) +{ + struct blk_mq_ctx *ctx = rq->mq_ctx; + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu); + + spin_lock(&hctx->lock); + list_add_tail(&rq->queuelist, &hctx->dispatch); + spin_unlock(&hctx->lock); + + blk_mq_run_hw_queue(hctx, false); +} + void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx, struct list_head *list) diff --git a/block/blk-mq.h b/block/blk-mq.h index 98252b79b80b..ef15b3414da5 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -54,6 +54,7 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, */ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, bool at_head); +void blk_mq_request_bypass_insert(struct request *rq); void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx, struct list_head *list);