linux-kernel - [PATCH 0/2] ipc/sem.c: sem

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Date:   Sat,  1 Oct 2016 20:40:15 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dave@...olabs.net>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
        1vier1@....de, felixh@...ormatik.uni-bremen.de,
        Manfred Spraul <manfred@...orfullife.com>
Subject: [PATCH 0/2] ipc/sem.c: sem_lock fixes

Hi Andrew, Hi Peter, Hi Davidlohr,

New idea for ipc/sem:
The ACQUIRE from spin_lock() will continue to apply only for the load,
not for the store.

Thus: If we don't want to add arch dependencies into ipc/sem, the only
safe option is to use spin_lock()/spin_unlock() instead of spin_unlock_wait().

Or we must stay with the current code, which is a ~9% regression.

Thus:
- Patch 1 replaces spin_unlock_wait() with spin_lock()/spin_unlock() and
  removes all memory barriers that are then unnecessary.

- Patch 2 adds the hysteresis code.

What do you think?

The patches passed stress-testing.

Andrew: Could you add it into mmots? Perhaps aiming for 4.10.

--
        Manfred