| Message ID | 20200129181253.24999-1-dave@stgolabs.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | rbd: optimize barrier usage for Rmw atomic bitops | expand |
On Wed, Jan 29, 2020 at 7:23 PM Davidlohr Bueso <dave@stgolabs.net> 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/block/rbd.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c > index 2b184563cd32..7bc79b2b8f65 100644 > --- a/drivers/block/rbd.c > +++ b/drivers/block/rbd.c > @@ -1371,13 +1371,13 @@ static void rbd_osd_submit(struct ceph_osd_request *osd_req) > static void img_request_layered_set(struct rbd_img_request *img_request) > { > set_bit(IMG_REQ_LAYERED, &img_request->flags); > - smp_mb(); > + smp_mb__after_atomic(); > } > > static void img_request_layered_clear(struct rbd_img_request *img_request) > { > clear_bit(IMG_REQ_LAYERED, &img_request->flags); > - smp_mb(); > + smp_mb__after_atomic(); > } > > static bool img_request_layered_test(struct rbd_img_request *img_request) Hi Davidlohr, I don't think these barriers are needed at all. I'll remove them. Thanks, Ilya
On Thu, 30 Jan 2020, Ilya Dryomov wrote:
>I don't think these barriers are needed at all. I'll remove them.
Even better, thanks.
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 2b184563cd32..7bc79b2b8f65 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -1371,13 +1371,13 @@ static void rbd_osd_submit(struct ceph_osd_request *osd_req) static void img_request_layered_set(struct rbd_img_request *img_request) { set_bit(IMG_REQ_LAYERED, &img_request->flags); - smp_mb(); + smp_mb__after_atomic(); } static void img_request_layered_clear(struct rbd_img_request *img_request) { clear_bit(IMG_REQ_LAYERED, &img_request->flags); - smp_mb(); + smp_mb__after_atomic(); } static bool img_request_layered_test(struct rbd_img_request *img_request)
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/block/rbd.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)