On 2012-08-07 11:22 Shaohua Li <shli@xxxxxxxxxx> Wrote:
>My directIO randomwrite 4k workload shows a 10~20% regression caused by commit
>895e3c5c58a80bb. directIO usually is random IO and if request size isn't big
>(which is the common case), delay handling of the stripe hasn't any advantages.
>For big size request, delay can still reduce IO.
>
>Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
>---
> drivers/md/raid5.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
>Index: linux/drivers/md/raid5.c
>===================================================================
>--- linux.orig/drivers/md/raid5.c 2012-08-07 11:04:48.442834682 +0800
>+++ linux/drivers/md/raid5.c 2012-08-07 11:09:08.743562203 +0800
>@@ -4076,6 +4076,7 @@ static void make_request(struct mddev *m
> struct stripe_head *sh;
> const int rw = bio_data_dir(bi);
> int remaining;
>+ bool large_request;
>
> if (unlikely(bi->bi_rw & REQ_FLUSH)) {
> md_flush_request(mddev, bi);
>@@ -4089,6 +4090,11 @@ static void make_request(struct mddev *m
> chunk_aligned_read(mddev,bi))
> return;
>
>+ if (mddev->new_chunk_sectors < mddev->chunk_sectors)
>+ large_request = (bi->bi_size >> 9) > mddev->new_chunk_sectors;
>+ else
>+ large_request = (bi->bi_size >> 9) > mddev->chunk_sectors;
>+
> logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
> last_sector = bi->bi_sector + (bi->bi_size>>9);
> bi->bi_next = NULL;
>@@ -4192,7 +4198,8 @@ static void make_request(struct mddev *m
> finish_wait(&conf->wait_for_overlap, &w);
> set_bit(STRIPE_HANDLE, &sh->state);
> clear_bit(STRIPE_DELAYED, &sh->state);
>- if ((bi->bi_rw & REQ_NOIDLE) &&
>+ if ((bi->bi_rw & REQ_SYNC) &&
>+ ((bi->bi_rw & REQ_NOIDLE) || !large_request) &&
> !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> atomic_inc(&conf->preread_active_stripes);
> release_stripe_plug(mddev, sh);
>--
May be used size to judge is not a good method.
I firstly sended this patch, only want to control direct-write-block,not for reqular file.
Because i think if someone used direct-write-block for raid5,he should know the feature of raid5 and he can control
for write to full-write.
But at that time, i did know how to differentiate between regular file and block-device.
I thik we should do something to do this.
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