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.
--
2.34.1
