On Mon, 16 Jul 2012 14:42:54 +0800 majianpeng <majianpeng@xxxxxxxxx> wrote: > On 2012-07-16 13:40 NeilBrown <neilb@xxxxxxx> Wrote: > >On Mon, 16 Jul 2012 09:31:55 +0800 majianpeng <majianpeng@xxxxxxxxx> wrote: > > > >> In commit e9c7469bb4f502dafc092166201bea1ad5fc0fbf: > >> Tejun Heo introduced "implment REQ_FLUSH/FUA support". > >> But for direct-write-blocks, it maybe for other purpose which like the > >> regular file. > >> And this flag will set STRIPE_PREREAD_ACTIVE which decreaed the change > >> to full write. > >> > >> But this patch remove REQ_SYNC only judging the WRITE_ODIRECT,it will > >> contail regular file.So it maybe not correctly. > >> How can difference odriect_write between regular file or block file? > > > >Hi, > > I think you are saying the when REQ_SYNC is used with O_DIRECT writes it is > > having a negative effect on throughput because it allows the stripe to be > > processed immediately without waiting for more requests to be added to the > > stripe. > > > > Normal 'sync' requests use WRITE_SYNC which includes "REQ_NOIDLE" which means > > /* don't anticipate more IO after this one */ > > O_DIRECT request use WRITE_ODIRECT which does not include this flag. > > > Using REQ_NOIDEL to difference odirect and sync.Why not using: > + if (bi->bi_rw & WRITE_ODIRECT) > + bi->bi_rw &= ~REQ_SYNC; Because that code is wrong. WRITE_ODIRECT is not one flag, it is two flags 'or'ed together. So this code does not do what you expect. > > The flag WRITE_ODIRECT is only used in odirect-write. > > > So maybe we should simply change raid5 to only set STRIPE_PREREAD_ACTIVE if > > REQ_NOIDLE is set on the bio. I think this would have the same effect as > > what you are trying to achieve. > > > > Could you please try that and see if it has the desired effect on > > performance? > > > I tested and the performance is the same. "The same" as what? The same are your original patch, or the same as without any patch? NeilBrown > >Thanks, > >NeilBrown > > > >i.e. something like this: > > > >diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > >index d56d74d..2d72a57 100644 > >--- a/drivers/md/raid5.c > >+++ b/drivers/md/raid5.c > >@@ -4178,7 +4178,7 @@ static void make_request(struct mddev *mddev, struct bio * bi) > > finish_wait(&conf->wait_for_overlap, &w); > > set_bit(STRIPE_HANDLE, &sh->state); > > clear_bit(STRIPE_DELAYED, &sh->state); > >- if ((bi->bi_rw & REQ_SYNC) && > >+ if ((bi->bi_rw & REQ_NOIDLE) && > > !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) > > atomic_inc(&conf->preread_active_stripes); > > release_stripe_plug(mddev, sh); > > > > > >> > >> Signed-off-by: Jianpeng Ma <majianpeng@xxxxxxxxx> > >> --- > >> drivers/md/raid5.c | 3 +++ > >> 1 files changed, 3 insertions(+), 0 deletions(-) > >> > >> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > >> index 04348d7..8d2d4d1 100644 > >> --- a/drivers/md/raid5.c > >> +++ b/drivers/md/raid5.c > >> @@ -4010,6 +4010,9 @@ static void make_request(struct mddev *mddev, struct bio * bi) > >> chunk_aligned_read(mddev,bi)) > >> return; > >> > >> + if (bi->bi_rw & WRITE_ODIRECT) > >> + bi->bi_rw &= ~REQ_SYNC; > >> + > >> logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1); > >> last_sector = bi->bi_sector + (bi->bi_size>>9); > >> bi->bi_next = NULL; > > > >
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