Date: Fri, 19 Mar 2004 10:50:47 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>
Subject: Re: [BENCHMARKS] 2.6.4 vs 2.6.4-mm1
Message-ID: <20040319095047.GA6301@elte.hu>
References: <40525C1F.5030705@cyberone.com.au>
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* Nick Piggin <piggin@cyberone.com.au> wrote:

> volanomark (MPS):
> This one starts getting huge mmap_sem contention at 150+ coming
> from futexes. Don't know what is taking the mmap_sem for writing.
> Maybe just brk or mmap.

are you sure it's down_write() contention? down_read() can create
contention just as much, simply due to the fact that hundreds of threads
and a dozen CPUs are pounding in on the same poor lock.

i do think there should be a rw-semaphore variant that is per-cpu for
the read path. (This would also fix the 4:4 threading overhead.)

	Ingo
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