| Message ID | 20110504082115.270298766@sli10-conroe.sh.intel.com |
|---|---|
| State | Not Applicable |
| Delegated to: | David Miller |
| Headers | show |
Hello, On Wed, May 04, 2011 at 04:17:27PM +0800, shaohua.li@intel.com wrote: > In some drives, flush requests are non-queueable. When flush request is running, > normal read/write requests can't run. If block layer dispatches such request, > driver can't handle it and requeue it. > Tejun suggested we can hold the queue when flush is running. This can avoid > unnecessary requeue. > Also this can improve performance. Say we have requests f1, w1, f2 (f is flush > request, and w is write request). When f1 is running, queue will be hold, so w1 > will not be added to queue list. Just after f1 is finished, f2 will be > dispatched. Since f1 already flushs cache out, f2 can be finished very quickly. > In my test, the queue holding completely solves a regression introduced by > commit 53d63e6b0dfb9588, which is about 20% regression running a sysbench fileio > workload. > > Signed-off-by: Shaohua Li <shaohua.li@intel.com> It looks good to me now, but some nitpicks. > Index: linux/block/blk-flush.c > =================================================================== > --- linux.orig/block/blk-flush.c 2011-05-04 14:20:33.000000000 +0800 > +++ linux/block/blk-flush.c 2011-05-04 15:23:50.000000000 +0800 > @@ -199,6 +199,9 @@ static void flush_end_io(struct request > > BUG_ON(q->flush_pending_idx == q->flush_running_idx); > > + queued |= q->flush_queue_delayed; > + q->flush_queue_delayed = 0; > + > /* account completion of the flush request */ > q->flush_running_idx ^= 1; > elv_completed_request(q, flush_rq); Can you please do if (queued || q->flush_queue_delayed) instead of setting queued? And please also update the comment above the if statement so that it explains the flush_queue_delayed case too. > Index: linux/block/blk.h > =================================================================== > --- linux.orig/block/blk.h 2011-05-04 14:20:33.000000000 +0800 > +++ linux/block/blk.h 2011-05-04 16:09:42.000000000 +0800 > @@ -61,7 +61,17 @@ static inline struct request *__elv_next > rq = list_entry_rq(q->queue_head.next); > return rq; > } > - > + /* > + * Flush request is running and flush request isn't queeueable > + * in the drive, we can hold the queue till flush request is > + * finished. Even we don't do this, driver can't dispatch next > + * requests and will requeue them. > + */ Please explain the f1, w1, f2 case here as that's the biggest reason this optimization is implemented and also explain the use of flush_queue_delayed (just explain briefly and refer to flush_end_io()). Thank you.
Hello. On 04-05-2011 12:17, shaohua.li@intel.com wrote: > In some drives, flush requests are non-queueable. When flush request is running, > normal read/write requests can't run. If block layer dispatches such request, > driver can't handle it and requeue it. > Tejun suggested we can hold the queue when flush is running. This can avoid > unnecessary requeue. > Also this can improve performance. Say we have requests f1, w1, f2 (f is flush > request, and w is write request). When f1 is running, queue will be hold, so w1 > will not be added to queue list. Just after f1 is finished, f2 will be > dispatched. Since f1 already flushs cache out, f2 can be finished very quickly. > In my test, the queue holding completely solves a regression introduced by > commit 53d63e6b0dfb9588, which is about 20% regression running a sysbench fileio Please specify that commit's summary -- for human readers. The ID is only immediately usable to gitweb. > workload. > Signed-off-by: Shaohua Li <shaohua.li@intel.com> [...] > Index: linux/block/blk.h > =================================================================== > --- linux.orig/block/blk.h 2011-05-04 14:20:33.000000000 +0800 > +++ linux/block/blk.h 2011-05-04 16:09:42.000000000 +0800 > @@ -61,7 +61,17 @@ static inline struct request *__elv_next > rq = list_entry_rq(q->queue_head.next); > return rq; > } > - > + /* > + * Flush request is running and flush request isn't queeueable Queueable. WBR, Sergei -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Index: linux/block/blk-flush.c =================================================================== --- linux.orig/block/blk-flush.c 2011-05-04 14:20:33.000000000 +0800 +++ linux/block/blk-flush.c 2011-05-04 15:23:50.000000000 +0800 @@ -199,6 +199,9 @@ static void flush_end_io(struct request BUG_ON(q->flush_pending_idx == q->flush_running_idx); + queued |= q->flush_queue_delayed; + q->flush_queue_delayed = 0; + /* account completion of the flush request */ q->flush_running_idx ^= 1; elv_completed_request(q, flush_rq); Index: linux/include/linux/blkdev.h =================================================================== --- linux.orig/include/linux/blkdev.h 2011-05-04 14:24:40.000000000 +0800 +++ linux/include/linux/blkdev.h 2011-05-04 14:29:29.000000000 +0800 @@ -365,6 +365,7 @@ struct request_queue */ unsigned int flush_flags; unsigned int flush_not_queueable:1; + unsigned int flush_queue_delayed:1; unsigned int flush_pending_idx:1; unsigned int flush_running_idx:1; unsigned long flush_pending_since; Index: linux/block/blk.h =================================================================== --- linux.orig/block/blk.h 2011-05-04 14:20:33.000000000 +0800 +++ linux/block/blk.h 2011-05-04 16:09:42.000000000 +0800 @@ -61,7 +61,17 @@ static inline struct request *__elv_next rq = list_entry_rq(q->queue_head.next); return rq; } - + /* + * Flush request is running and flush request isn't queeueable + * in the drive, we can hold the queue till flush request is + * finished. Even we don't do this, driver can't dispatch next + * requests and will requeue them. + */ + if (q->flush_pending_idx != q->flush_running_idx && + !blk_queue_flush_queueable(q)) { + q->flush_queue_delayed = 1; + return NULL; + } if (!q->elevator->ops->elevator_dispatch_fn(q, 0)) return NULL; }
In some drives, flush requests are non-queueable. When flush request is running, normal read/write requests can't run. If block layer dispatches such request, driver can't handle it and requeue it. Tejun suggested we can hold the queue when flush is running. This can avoid unnecessary requeue. Also this can improve performance. Say we have requests f1, w1, f2 (f is flush request, and w is write request). When f1 is running, queue will be hold, so w1 will not be added to queue list. Just after f1 is finished, f2 will be dispatched. Since f1 already flushs cache out, f2 can be finished very quickly. In my test, the queue holding completely solves a regression introduced by commit 53d63e6b0dfb9588, which is about 20% regression running a sysbench fileio workload. Signed-off-by: Shaohua Li <shaohua.li@intel.com> --- block/blk-flush.c | 3 +++ block/blk.h | 12 +++++++++++- include/linux/blkdev.h | 1 + 3 files changed, 15 insertions(+), 1 deletion(-) -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html