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

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Message-Id: <20160713150525.8f703dfa5e83a534f8a51106@linux-foundation.org>
Date:	Wed, 13 Jul 2016 15:05:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, 1vier1@....de,
	felixh@...ormatik.uni-bremen.de
Subject: Re: [PATCH 0/2] ipc/sem.c: sem_lock fixes

On Wed, 13 Jul 2016 07:06:50 +0200 Manfred Spraul <manfred@...orfullife.com> wrote:

> Hi Andrew, Hi Peter,
> 
> next version of the sem_lock() fixes:
> The patches are again vs. tip.
> 
> Patch 1 is ready for merging, Patch 2 is for review.
> 
> - Patch 1 is the patch as in -next since January
>   It fixes the race that was found by Felix.
> - Patch 2 removes the memory barriers that are part of the qspinlock
>   code.
> - (The hysteresis patch would be patch 3. The risk of regressions
>   can't be ruled out, thus it must wait for benchmarks from real
>   workload tests)

I think you're saying that if these two patches cause performance
regressions, we will need ipc-sem-sem_lock-with-hysteresis.patch?

Is that even necessary?  If your testing shows that
ipc-sem-sem_lock-with-hysteresis.patch makes things faster then in it
goes, surely?