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From: Sunil Pandey <skpgkp2@sourceware.org>
To: glibc-cvs@sourceware.org
Subject: [glibc/users/skpgkp2/2.33/master] nptl: Effectively skip CAS in spinlock loop
Date: Wed, 28 Sep 2022 21:45:52 +0000 (GMT)	[thread overview]
Message-ID: <20220928214552.D707E3858403@sourceware.org> (raw)

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=49479d237f678b53700689085e075d1382e401de

commit 49479d237f678b53700689085e075d1382e401de
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
    
    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>
    (cherry picked from commit 6b8dbbd03ac88f169b65b5c7d7278576a11d2e44)

Diff:
---
 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 2895926953..253743f76c 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -138,10 +138,9 @@ __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;
 	}

             reply	other threads:[~2022-09-28 21:45 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-28 21:45 Sunil Pandey [this message]
  -- strict thread matches above, loose matches on Subject: below --
2022-09-29 18:41 Sunil Pandey
2022-09-28 19:11 Sunil Pandey

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