| Message ID | 20230710180210.1582299-2-bvanassche@acm.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Enable zoned write pipelining for UFS devices | expand |
On 7/11/23 03:01, Bart Van Assche wrote: > Writes in sequential write required zones must happen at the write > pointer. Even if the submitter of the write commands (e.g. a filesystem) > submits writes for sequential write required zones in order, the block > layer or the storage controller may reorder these write commands. > > The zone locking mechanism in the mq-deadline I/O scheduler serializes > write commands for sequential zones. Some but not all storage controllers > require this serialization. Introduce a new flag such that block drivers > can request pipelining of writes for sequential write required zones. > > An example of a storage controller standard that requires write > serialization is AHCI (Advanced Host Controller Interface). Submitting > commands to AHCI controllers happens by writing a bit pattern into a > register. Each set bit corresponds to an active command. This mechanism > does not preserve command ordering information. > > Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com> > Signed-off-by: Bart Van Assche <bvanassche@acm.org> > --- > include/linux/blkdev.h | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index ed44a997f629..805012c5a6ab 100644 > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -534,6 +534,8 @@ struct request_queue { > #define QUEUE_FLAG_NONROT 6 /* non-rotational device (SSD) */ > #define QUEUE_FLAG_VIRT QUEUE_FLAG_NONROT /* paravirt device */ > #define QUEUE_FLAG_IO_STAT 7 /* do disk/partitions IO accounting */ > +/* Writes for sequential write required zones may be pipelined. */ > +#define QUEUE_FLAG_PIPELINE_ZONED_WRITES 8 I am not a big fan of this name as "pipeline" does not necessarily imply "high queue depth write". What about simply calling this QUEUE_FLAG_NO_ZONE_WRITE_LOCK, indicating that there is no need to write-lock zones ? > #define QUEUE_FLAG_NOXMERGES 9 /* No extended merges */ > #define QUEUE_FLAG_ADD_RANDOM 10 /* Contributes to random pool */ > #define QUEUE_FLAG_SYNCHRONOUS 11 /* always completes in submit context */ > @@ -596,6 +598,11 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q); > #define blk_queue_skip_tagset_quiesce(q) \ > test_bit(QUEUE_FLAG_SKIP_TAGSET_QUIESCE, &(q)->queue_flags) > > +static inline bool blk_queue_pipeline_zoned_writes(struct request_queue *q) > +{ > + return test_bit(QUEUE_FLAG_PIPELINE_ZONED_WRITES, &q->queue_flags); > +} > + > extern void blk_set_pm_only(struct request_queue *q); > extern void blk_clear_pm_only(struct request_queue *q); >
On 7/17/23 23:34, Damien Le Moal wrote: > On 7/11/23 03:01, Bart Van Assche wrote: >> +/* Writes for sequential write required zones may be pipelined. */ >> +#define QUEUE_FLAG_PIPELINE_ZONED_WRITES 8 > > I am not a big fan of this name as "pipeline" does not necessarily imply "high > queue depth write". What about simply calling this > QUEUE_FLAG_NO_ZONE_WRITE_LOCK, indicating that there is no need to write-lock > zones ? Hi Damien, I'm not a big fan of names with negative words like "no" or "not" embedded. Isn't pipelining standard computer science terminology? See also https://en.wikipedia.org/wiki/Pipeline_(computing). Thanks, Bart.
On 7/19/23 07:37, Bart Van Assche wrote: > On 7/17/23 23:34, Damien Le Moal wrote: >> On 7/11/23 03:01, Bart Van Assche wrote: >>> +/* Writes for sequential write required zones may be pipelined. */ >>> +#define QUEUE_FLAG_PIPELINE_ZONED_WRITES 8 >> >> I am not a big fan of this name as "pipeline" does not necessarily >> imply "high >> queue depth write". What about simply calling this >> QUEUE_FLAG_NO_ZONE_WRITE_LOCK, indicating that there is no need to >> write-lock >> zones ? > > Hi Damien, > > I'm not a big fan of names with negative words like "no" or "not" embedded. > Isn't pipelining standard computer science terminology? See also > https://en.wikipedia.org/wiki/Pipeline_(computing). Sure, pipeline is a well known term. But I do not think it is synonymous with "high queue depth write" :) A "pipeline" for zoned write may still operate at write qd=1 per zone... Given that the default is using zone write locking, I would prefer a flag name that indicates a change to this default. What about something like QUEUE_FLAG_UNRESTRICTED_ZONE_WRITE ? But tht is beside the point as I still have reservations on this approach anyway. See my reply to patch 4.
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index ed44a997f629..805012c5a6ab 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -534,6 +534,8 @@ struct request_queue { #define QUEUE_FLAG_NONROT 6 /* non-rotational device (SSD) */ #define QUEUE_FLAG_VIRT QUEUE_FLAG_NONROT /* paravirt device */ #define QUEUE_FLAG_IO_STAT 7 /* do disk/partitions IO accounting */ +/* Writes for sequential write required zones may be pipelined. */ +#define QUEUE_FLAG_PIPELINE_ZONED_WRITES 8 #define QUEUE_FLAG_NOXMERGES 9 /* No extended merges */ #define QUEUE_FLAG_ADD_RANDOM 10 /* Contributes to random pool */ #define QUEUE_FLAG_SYNCHRONOUS 11 /* always completes in submit context */ @@ -596,6 +598,11 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q); #define blk_queue_skip_tagset_quiesce(q) \ test_bit(QUEUE_FLAG_SKIP_TAGSET_QUIESCE, &(q)->queue_flags) +static inline bool blk_queue_pipeline_zoned_writes(struct request_queue *q) +{ + return test_bit(QUEUE_FLAG_PIPELINE_ZONED_WRITES, &q->queue_flags); +} + extern void blk_set_pm_only(struct request_queue *q); extern void blk_clear_pm_only(struct request_queue *q);
Writes in sequential write required zones must happen at the write pointer. Even if the submitter of the write commands (e.g. a filesystem) submits writes for sequential write required zones in order, the block layer or the storage controller may reorder these write commands. The zone locking mechanism in the mq-deadline I/O scheduler serializes write commands for sequential zones. Some but not all storage controllers require this serialization. Introduce a new flag such that block drivers can request pipelining of writes for sequential write required zones. An example of a storage controller standard that requires write serialization is AHCI (Advanced Host Controller Interface). Submitting commands to AHCI controllers happens by writing a bit pattern into a register. Each set bit corresponds to an active command. This mechanism does not preserve command ordering information. Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com> Signed-off-by: Bart Van Assche <bvanassche@acm.org> --- include/linux/blkdev.h | 7 +++++++ 1 file changed, 7 insertions(+)