| Message ID | aa518c5b5c7185e660a1c8515c10d9513fe92132.1607591591.git.baolin.wang@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] blk-iocost: Add iocg idle state tracepoint | expand |
Hello, On Thu, Dec 10, 2020 at 06:56:45PM +0800, Baolin Wang wrote: > Use alloc_percpu_gfp() with __GFP_ZERO flag, which can remove > some explicit initialization code. __GFP_ZERO is implicit for percpu allocations and local[64]_t's initial states aren't guaranteed to be all zeros on different archs. Thanks.
Hi Tejun, > Hello, > > On Thu, Dec 10, 2020 at 06:56:45PM +0800, Baolin Wang wrote: >> Use alloc_percpu_gfp() with __GFP_ZERO flag, which can remove >> some explicit initialization code. > > __GFP_ZERO is implicit for percpu allocations and local[64]_t's initial > states aren't guaranteed to be all zeros on different archs. Thanks for teaching me this, at least I did not get this from the local_ops Documentation before. Just out of curiosity, these local[64]_t variables are also allocated from budy allocator ultimately, why they can not be initialized to zeros on some ARCHs with __GFP_ZERO? Could you elaborate on about this restriction? Thanks. By the way, seems the kyber-iosched has the same issue, since the 'struct kyber_cpu_latency' also contains an atomic_t variable. kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency, GFP_KERNEL | __GFP_ZERO); if (!kqd->cpu_latency) goto err_kqd;
Hello, On Fri, Dec 11, 2020 at 03:13:29PM +0800, Baolin Wang wrote: > Thanks for teaching me this, at least I did not get this from the local_ops > Documentation before. Just out of curiosity, these local[64]_t variables are > also allocated from budy allocator ultimately, why they can not be > initialized to zeros on some ARCHs with __GFP_ZERO? Could you elaborate on > about this restriction? Thanks. * It's highly unlikely but theoretically possible that some arch might need more than raw value to implement local semantics. * People might wanna add debug annotations which may require more than just the raw value. > By the way, seems the kyber-iosched has the same issue, since the 'struct > kyber_cpu_latency' also contains an atomic_t variable. > > kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency, > GFP_KERNEL | __GFP_ZERO); > if (!kqd->cpu_latency) > goto err_kqd; Yeah, the lines become blurry when all existing usages are fine with zeroing and we do end up needing to clean up those when the need arises (e.g. we used to zero some spinlocks too). It's just a better form to stick with initializers when they are provided. Thanks.
Hi Tejun, > Hello, > > On Fri, Dec 11, 2020 at 03:13:29PM +0800, Baolin Wang wrote: >> Thanks for teaching me this, at least I did not get this from the local_ops >> Documentation before. Just out of curiosity, these local[64]_t variables are >> also allocated from budy allocator ultimately, why they can not be >> initialized to zeros on some ARCHs with __GFP_ZERO? Could you elaborate on >> about this restriction? Thanks. > > * It's highly unlikely but theoretically possible that some arch might need > more than raw value to implement local semantics. > > * People might wanna add debug annotations which may require more than just > the raw value. Thanks for your explanation. It will be helpful to add these comments for the code in case someone else wants to do the same thing like this patch in future. I can send a patch to add these comments if you have no objection. >> By the way, seems the kyber-iosched has the same issue, since the 'struct >> kyber_cpu_latency' also contains an atomic_t variable. >> >> kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency, >> GFP_KERNEL | __GFP_ZERO); >> if (!kqd->cpu_latency) >> goto err_kqd; > > Yeah, the lines become blurry when all existing usages are fine with zeroing > and we do end up needing to clean up those when the need arises (e.g. we > used to zero some spinlocks too). It's just a better form to stick with > initializers when they are provided. OK. Sounds it is worth sending a patch to initialize this structure explicitly to keep consistent.
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index ac6078a..52ce2e3 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -2819,28 +2819,19 @@ static int blk_iocost_init(struct request_queue *q) { struct ioc *ioc; struct rq_qos *rqos; - int i, cpu, ret; + int ret; + gfp_t gfp = GFP_KERNEL | __GFP_ZERO; ioc = kzalloc(sizeof(*ioc), GFP_KERNEL); if (!ioc) return -ENOMEM; - ioc->pcpu_stat = alloc_percpu(struct ioc_pcpu_stat); + ioc->pcpu_stat = alloc_percpu_gfp(struct ioc_pcpu_stat, gfp); if (!ioc->pcpu_stat) { kfree(ioc); return -ENOMEM; } - for_each_possible_cpu(cpu) { - struct ioc_pcpu_stat *ccs = per_cpu_ptr(ioc->pcpu_stat, cpu); - - for (i = 0; i < ARRAY_SIZE(ccs->missed); i++) { - local_set(&ccs->missed[i].nr_met, 0); - local_set(&ccs->missed[i].nr_missed, 0); - } - local64_set(&ccs->rq_wait_ns, 0); - } - rqos = &ioc->rqos; rqos->id = RQ_QOS_COST; rqos->ops = &ioc_rqos_ops;
Use alloc_percpu_gfp() with __GFP_ZERO flag, which can remove some explicit initialization code. Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> --- block/blk-iocost.c | 15 +++------------ 1 file changed, 3 insertions(+), 12 deletions(-)