Messages in this thread Patch in this message | | | Subject | Re: [PATCH] md: optimize barrier usage for Rmw atomic bitops | From | Guoqing Jiang <> | Date | Fri, 31 Jan 2020 17:43:34 +0100 |
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On 1/29/20 7:14 PM, Davidlohr Bueso wrote: > For both set and clear_bit, we can avoid the unnecessary barrier > on non LL/SC architectures, such as x86. Instead, use the > smp_mb__{before,after}_atomic() calls. > > Signed-off-by: Davidlohr Bueso <dbueso@suse.de> > --- > drivers/md/md.c | 2 +- > drivers/md/raid10.c | 7 ++++--- > drivers/md/raid5.c | 9 +++++---- > 3 files changed, 10 insertions(+), 8 deletions(-) > > diff --git a/drivers/md/md.c b/drivers/md/md.c > index 4824d50526fa..4ed2eb6933f7 100644 > --- a/drivers/md/md.c > +++ b/drivers/md/md.c > @@ -2561,7 +2561,7 @@ static bool set_in_sync(struct mddev *mddev) > * Ensure ->in_sync is visible before we clear > * ->sync_checkers. > */ > - smp_mb(); > + smp_mb__before_atomic(); > set_bit(MD_SB_CHANGE_CLEAN, &mddev->sb_flags); > sysfs_notify_dirent_safe(mddev->sysfs_state); > } > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c > index ec136e44aef7..1993a1958c75 100644 > --- a/drivers/md/raid10.c > +++ b/drivers/md/raid10.c > @@ -1865,9 +1865,10 @@ static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev) > /* We must have just cleared 'rdev' */ > p->rdev = p->replacement; > clear_bit(Replacement, &p->replacement->flags); > - smp_mb(); /* Make sure other CPUs may see both as identical > - * but will never see neither -- if they are careful. > - */ > + /* Make sure other CPUs may see both as identical > + * but will never see neither -- if they are careful. > + */
Since we are here, it is better to change the comment style to
/* * ... */
> + smp_mb__after_atomic(); > p->replacement = NULL; > } > > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > index ba00e9877f02..3ad6209287cf 100644 > --- a/drivers/md/raid5.c > +++ b/drivers/md/raid5.c > @@ -364,7 +364,7 @@ static int release_stripe_list(struct r5conf *conf, > int hash; > > /* sh could be readded after STRIPE_ON_RELEASE_LIST is cleard */ > - smp_mb(); > + smp_mb__before_atomic(); > clear_bit(STRIPE_ON_RELEASE_LIST, &sh->state); > /* > * Don't worry the bit is set here, because if the bit is set > @@ -7654,9 +7654,10 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev) > /* We must have just cleared 'rdev' */ > p->rdev = p->replacement; > clear_bit(Replacement, &p->replacement->flags); > - smp_mb(); /* Make sure other CPUs may see both as identical > - * but will never see neither - if they are careful > - */
Ditto.
Acked-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Thanks, Guoqing
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