From: Manfred Spraul <manfred@colorfullife.com>
To: "H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Davidlohr Bueso <dave@stgolabs.net>
Cc: LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
1vier1@web.de, felixh@informatik.uni-bremen.de,
Manfred Spraul <manfred@colorfullife.com>
Subject: [PATCH 0/2] ipc/sem.c: sem_lock fixes
Date: Sat, 25 Jun 2016 19:37:50 +0200 [thread overview]
Message-ID: <1466876272-3824-1-git-send-email-manfred@colorfullife.com> (raw)
Hi Andrew, Hi Peter,
next version of the sem_lock() fixes / improvement:
The patches are now vs. tip.
Patch 1 is ready for merging, patch 2 is new and for discussion.
Patch 1 fixes the race that was found by Felix.
It also adds smp_mb() to fully synchronize
WRITE_ONCE(status, 1);
<<< smp_mb();
spin_unlock_wait();
vs.
spin_lock();
<<< smp_mb();
READ_ONCE(status);
Patch 2 tries to close a performance regression:
sem_wait_array() must perform a spin_unlock_wait() for every
semaphore in the array. If the array is large, then this is
slow.
Two open points:
- Do we need it? Factor 20 improvement is nice, but is the
test realistic?
- COMPLEX_MODE_ENTER=10 is a magic number, without any
rational. (2+sem_nsems/128) would be another option,
but also arbitrary.
Test:
https://github.com/manfred-colorfu/ipcscale
# ./sem-scalebench -o 4 -f -m 0 -h 4 -i 1 -p 2 -c 8 -t 5 -d 500
Before: 214732
After: 4008635
--
Manfred
next reply other threads:[~2016-06-25 17:38 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-25 17:37 Manfred Spraul [this message]
2016-06-25 17:37 ` [PATCH 1/2] ipc/sem.c: Fix complex_count vs. simple op race Manfred Spraul
2016-06-25 17:37 ` [PATCH 2/2] ipc/sem: sem_lock with hysteresis Manfred Spraul
2016-07-13 5:06 [PATCH 0/2] ipc/sem.c: sem_lock fixes Manfred Spraul
2016-07-13 22:05 ` Andrew Morton
2016-07-14 16:40 ` Manfred Spraul
2016-10-01 18:40 Manfred Spraul
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