From: Alan Huang <mmpgouride@gmail.com>
To: paulmck@kernel.org
Cc: perfbook@vger.kernel.org, Alan Huang <mmpgouride@gmail.com>
Subject: [PATCH] CodeSamples/count: change full memory barrier to partial one
Date: Tue, 4 Apr 2023 01:19:21 -0400 [thread overview]
Message-ID: <20230404051921.1305092-1-mmpgouride@gmail.com> (raw)
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.
In count_lim_sig.c, there is only one ordering required, that is
writing to counter happens before setting theft to THEFT_READY in
add_count/sub_count's fast path. Therefore, partial memory barrier
will suffice.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
---
CodeSamples/count/count_lim_sig.c | 10 +++-------
CodeSamples/count/count_stat_eventual.c | 6 ++----
2 files changed, 5 insertions(+), 11 deletions(-)
diff --git a/CodeSamples/count/count_lim_sig.c b/CodeSamples/count/count_lim_sig.c
index 59da8077..c2f61197 100644
--- a/CodeSamples/count/count_lim_sig.c
+++ b/CodeSamples/count/count_lim_sig.c
@@ -56,12 +56,10 @@ static void flush_local_count_sig(int unused) //\lnlbl{flush_sig:b}
{
if (READ_ONCE(theft) != THEFT_REQ) //\lnlbl{flush_sig:check:REQ}
return; //\lnlbl{flush_sig:return:n}
- smp_mb(); //\lnlbl{flush_sig:mb:1}
WRITE_ONCE(theft, THEFT_ACK); //\lnlbl{flush_sig:set:ACK}
if (!counting) { //\lnlbl{flush_sig:check:fast}
- WRITE_ONCE(theft, THEFT_READY); //\lnlbl{flush_sig:set:READY}
+ smp_store_release(&theft, THEFT_READY); //\lnlbl{flush_sig:set:READY}
}
- smp_mb();
} //\lnlbl{flush_sig:e}
static void flush_local_count(void) //\lnlbl{flush:b}
@@ -125,8 +123,7 @@ int add_count(unsigned long delta) //\lnlbl{b}
WRITE_ONCE(counting, 0); //\lnlbl{clearcnt}
barrier(); //\lnlbl{barrier:3}
if (READ_ONCE(theft) == THEFT_ACK) { //\lnlbl{check:ACK}
- smp_mb(); //\lnlbl{mb}
- WRITE_ONCE(theft, THEFT_READY); //\lnlbl{READY}
+ smp_store_release(&theft, THEFT_READY); //\lnlbl{READY}
}
if (fastpath)
return 1; //\lnlbl{return:fs}
@@ -164,8 +161,7 @@ int sub_count(unsigned long delta)
WRITE_ONCE(counting, 0);
barrier();
if (READ_ONCE(theft) == THEFT_ACK) {
- smp_mb();
- WRITE_ONCE(theft, THEFT_READY);
+ smp_store_release(&theft, THEFT_READY);
}
if (fastpath)
return 1;
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}
--
2.34.1
next reply other threads:[~2023-04-04 5:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-04 5:19 Alan Huang [this message]
2023-04-04 11:28 ` [PATCH] CodeSamples/count: change full memory barrier to partial one Akira Yokosawa
2023-04-04 15:07 ` Alan Huang
2023-04-04 15:14 ` Alan Huang
-- strict thread matches above, loose matches on Subject: below --
2023-04-05 16:56 Alan Huang
2023-04-06 0:09 ` Akira Yokosawa
2023-04-06 18:26 ` Paul E. McKenney
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