* Re: [PATCH v4] nptl: Effectively skip CAS in spinlock loop [not found] ` <YelevLkTZU5Kb4Xi@gmail.com> @ 2022-09-11 20:23 ` Sunil Pandey 2022-09-29 0:11 ` Noah Goldstein 0 siblings, 1 reply; 2+ messages in thread From: Sunil Pandey @ 2022-09-11 20:23 UTC (permalink / raw) To: H.J. Lu, Libc-stable Mailing List, Florian Weimer Cc: Jangwoong Kim, GNU C Library On Thu, Jan 20, 2022 at 5:08 AM H.J. Lu via Libc-alpha <libc-alpha@sourceware.org> wrote: > > 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 > I would like to backport this patch to release branch 2.33 and 2.34 Any comments/suggestions or objections on this. commit 6b8dbbd03ac88f169b65b5c7d7278576a11d2e44 Author: Jangwoong Kim <6812skiii@gmail.com> Date: Tue Dec 14 21:30:51 2021 +0900 nptl: Effectively skip CAS in spinlock loop The commit: "Add LLL_MUTEX_READ_LOCK [BZ #28537]" SHA1: d672a98a1af106bd68deb15576710cd61363f7a6 ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v4] nptl: Effectively skip CAS in spinlock loop 2022-09-11 20:23 ` [PATCH v4] nptl: Effectively skip CAS in spinlock loop Sunil Pandey @ 2022-09-29 0:11 ` Noah Goldstein 0 siblings, 0 replies; 2+ messages in thread From: Noah Goldstein @ 2022-09-29 0:11 UTC (permalink / raw) To: Sunil Pandey Cc: H.J. Lu, Libc-stable Mailing List, Florian Weimer, Jangwoong Kim, GNU C Library On Sun, Sep 11, 2022 at 4:24 PM Sunil Pandey via Libc-stable <libc-stable@sourceware.org> wrote: > > On Thu, Jan 20, 2022 at 5:08 AM H.J. Lu via Libc-alpha > <libc-alpha@sourceware.org> wrote: > > > > 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 > > > > I would like to backport this patch to release branch 2.33 and 2.34 Fine by me. > > Any comments/suggestions or objections on this. > > commit 6b8dbbd03ac88f169b65b5c7d7278576a11d2e44 > Author: Jangwoong Kim <6812skiii@gmail.com> > Date: Tue Dec 14 21:30:51 2021 +0900 > > nptl: Effectively skip CAS in spinlock loop > > The commit: > "Add LLL_MUTEX_READ_LOCK [BZ #28537]" > SHA1: d672a98a1af106bd68deb15576710cd61363f7a6 ^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-09-11 20:23 ` [PATCH v4] nptl: Effectively skip CAS in spinlock loop Sunil Pandey
2022-09-29 0:11 ` Noah Goldstein
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