On Thu, Apr 06, 2023 at 09:09:22AM +0900, Akira Yokosawa wrote:
> On Wed, 5 Apr 2023 12:56:41 -0400, Alan Huang wrote:
> > The original memory barriers in count_stat_eventual.c ensure
> > writing to global_count happens before writing to stopflag and
> > reading from stopflag happens before later reading from global_count.
> >
> > Thus, smp_load_acquire and smp_store_release will suffice.
> >
> > Signed-off-by: Alan Huang <mmpgouride@xxxxxxxxx>
> > ---
> > CodeSamples/count/count_stat_eventual.c | 6 ++----
> > count/count.tex | 6 +++---
> > 2 files changed, 5 insertions(+), 7 deletions(-)
> >
> > diff --git a/CodeSamples/count/count_stat_eventual.c b/CodeSamples/count/count_stat_eventual.c
> > index 967644de..7157ee0e 100644
> > --- a/CodeSamples/count/count_stat_eventual.c
> > +++ b/CodeSamples/count/count_stat_eventual.c
> > @@ -51,8 +51,7 @@ void *eventual(void *arg) //\lnlbl{eventual:b}
> > WRITE_ONCE(global_count, sum);
> > poll(NULL, 0, 1);
> > if (READ_ONCE(stopflag)) {
> > - smp_mb();
> > - WRITE_ONCE(stopflag, stopflag + 1);
> > + smp_store_release(&stopflag, stopflag + 1);
> > }
> > }
> > return NULL;
> > @@ -73,9 +72,8 @@ void count_init(void) //\lnlbl{init:b}
> > void count_cleanup(void) //\lnlbl{cleanup:b}
> > {
> > WRITE_ONCE(stopflag, 1);
> > - while (READ_ONCE(stopflag) < 3)
> > + while (smp_load_acquire(&stopflag) < 3)
> > poll(NULL, 0, 1);
> > - smp_mb();
> > } //\lnlbl{cleanup:e}
> > //\end{snippet}
> >
> > diff --git a/count/count.tex b/count/count.tex
> > index 80ada104..8ab67e2e 100644
> > --- a/count/count.tex
> > +++ b/count/count.tex
> > @@ -1013,9 +1013,9 @@ between passes.
> >
> > The \co{count_cleanup()} function on
> > \clnrefrange{cleanup:b}{cleanup:e} coordinates termination.
> > -The calls to \co{smp_mb()} here and in \co{eventual()} ensure
> > -that all updates to \co{global_count} are visible to code following
> > -the call to \co{count_cleanup()}.
> > +The call to \co{smp_load_acquire()} here and the call to \co{smp_store_release()}
> > +in \co{eventual()} ensure that all updates to \co{global_count} are visible
> > +to code following the call to \co{count_cleanup()}.
> >
> > This approach gives extremely fast counter read-out while still
> > supporting linear counter-update scalability.
>
> Looks good to me! Thanks.
>
> Reviewed-by: Akira Yokosawa <akiyks@xxxxxxxxx>
Queued and pushed with the inevitable wordsmithing, thank you both!
Thanx, Paul
