From: "H.J. Lu" <hjl.tools@gmail.com>
To: Jangwoong Kim <6812skiii@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: [PATCH v4] nptl: Effectively skip CAS in spinlock loop
Date: Thu, 20 Jan 2022 05:08:12 -0800 [thread overview]
Message-ID: <YelevLkTZU5Kb4Xi@gmail.com> (raw)
In-Reply-To: <CAMe9rOpG1M8t3+dkJS5tYt-qzdW+rMmvQBW5rdExUOSCpFUbJg@mail.gmail.com>
On Thu, Jan 20, 2022 at 04:53:27AM -0800, H.J. Lu wrote:
> On Tue, Dec 14, 2021 at 4:31 AM Jangwoong Kim via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > The commit:
> > "Add LLL_MUTEX_READ_LOCK [BZ #28537]"
> > SHA1: d672a98a1af106bd68deb15576710cd61363f7a6
> >
> > introduced LLL_MUTEX_READ_LOCK, to skip CAS in spinlock loop
> > if atomic load fails. But, "continue" inside of do-while loop
> > does not skip the evaluation of escape expression, thus CAS
> > is not skipped.
> >
> > Replace do-while with while and skip LLL_MUTEX_TRYLOCK if
> > LLL_MUTEX_READ_LOCK fails.
> > ---
> > nptl/pthread_mutex_lock.c | 5 +----
> > 1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
> > index 47b88a6b5b..06274c68e4 100644
> > --- a/nptl/pthread_mutex_lock.c
> > +++ b/nptl/pthread_mutex_lock.c
> > @@ -138,7 +138,7 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
> > int cnt = 0;
> > int max_cnt = MIN (max_adaptive_count (),
> > mutex->__data.__spins * 2 + 10);
> > - do
> > + while (LLL_MUTEX_READ_LOCK (mutex) != 0 || LLL_MUTEX_TRYLOCK (mutex) != 0)
> > {
> > if (cnt++ >= max_cnt)
> > {
> > @@ -146,10 +146,7 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
> > break;
> > }
> > atomic_spin_nop ();
> > - if (LLL_MUTEX_READ_LOCK (mutex) != 0)
> > - continue;
> > }
> > - while (LLL_MUTEX_TRYLOCK (mutex) != 0);
> >
> > mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
> > }
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
This is the v4 patch I am checkinng in.
H.J.
---
From: Jangwoong Kim <6812skiii@gmail.com>
Date: Tue, 14 Dec 2021 21:30:51 +0900
The commit:
"Add LLL_MUTEX_READ_LOCK [BZ #28537]"
SHA1: d672a98a1af106bd68deb15576710cd61363f7a6
introduced LLL_MUTEX_READ_LOCK, to skip CAS in spinlock loop
if atomic load fails. But, "continue" inside of do-while loop
does not skip the evaluation of escape expression, thus CAS
is not skipped.
Replace do-while with while and skip LLL_MUTEX_TRYLOCK if
LLL_MUTEX_READ_LOCK fails.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
nptl/pthread_mutex_lock.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 31dfc7f1d7..d2e652d151 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -146,10 +146,9 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
break;
}
atomic_spin_nop ();
- if (LLL_MUTEX_READ_LOCK (mutex) != 0)
- continue;
}
- while (LLL_MUTEX_TRYLOCK (mutex) != 0);
+ while (LLL_MUTEX_READ_LOCK (mutex) != 0
+ || LLL_MUTEX_TRYLOCK (mutex) != 0);
mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
}
--
2.34.1
next prev parent reply other threads:[~2022-01-20 13:08 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-14 12:30 [PATCH v3] " Jangwoong Kim
2022-01-20 12:53 ` H.J. Lu
2022-01-20 13:08 ` H.J. Lu [this message]
2022-09-11 20:23 ` [PATCH v4] " Sunil Pandey
2022-09-29 0:11 ` Noah Goldstein
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