From: Nick Piggin <npiggin@suse.de>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Eric Dumazet <dada1@cosmosbay.com>, Ingo Molnar <mingo@elte.hu>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Oleg Nesterov <oleg@tv-sign.ru>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 0/2] convert mmap_sem to a scalable rw_mutex
Date: Mon, 14 May 2007 14:07:37 +0200 [thread overview]
Message-ID: <20070514120737.GE31234@wotan.suse.de> (raw)
In-Reply-To: <1178903913.2781.20.camel@lappy>
On Fri, May 11, 2007 at 07:18:33PM +0200, Peter Zijlstra wrote:
> On Fri, 2007-05-11 at 18:52 +0200, Eric Dumazet wrote:
> >
> > But I personally find this new rw_mutex not scalable at all if you have some
> > writers around.
> >
> > percpu_counter_sum is just a L1 cache eater, and O(NR_CPUS)
>
> Yeah, that is true; there are two occurences, the one in
> rw_mutex_read_unlock() is not strictly needed for correctness.
>
> Write locks are indeed quite expensive. But given the ratio of
> reader:writer locks on mmap_sem (I'm not all that familiar with other
> rwsem users) this trade-off seems workable.
I guess the problem with that logic is assuming the mmap_sem read side
always needs to be scalable. Given the ratio of threaded:unthreaded
apps, maybe the trade-off swings away from favour?
--
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next prev parent reply other threads:[~2007-05-14 12:07 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-11 13:15 Peter Zijlstra
2007-05-11 13:15 ` [PATCH 1/2] " Peter Zijlstra
2007-05-11 14:03 ` Christoph Hellwig
2007-05-11 16:31 ` Andrew Morton
2007-05-11 17:07 ` Christoph Lameter
2007-05-11 18:05 ` Andrew Morton
2007-05-12 18:55 ` Andi Kleen
2007-05-12 18:06 ` Andrew Morton
2007-05-12 18:11 ` Andrew Morton
2007-05-16 23:28 ` Andrew Morton
2007-05-16 23:40 ` Christoph Lameter
2007-05-17 0:24 ` Andrew Morton
2007-05-12 18:12 ` Oleg Nesterov
2007-05-12 19:21 ` Andi Kleen
2007-05-12 21:42 ` Oleg Nesterov
2007-05-11 17:57 ` Peter Zijlstra
2007-05-11 23:00 ` Oleg Nesterov
2007-05-12 7:39 ` Peter Zijlstra
2007-05-12 13:41 ` Peter Zijlstra
2007-05-12 16:04 ` Oleg Nesterov
2007-05-12 16:57 ` Peter Zijlstra
2007-05-12 18:03 ` Oleg Nesterov
2007-05-14 10:59 ` Peter Zijlstra
2007-05-14 11:36 ` Nick Piggin
2007-05-15 0:36 ` Paul E. McKenney
2007-05-15 7:43 ` Peter Zijlstra
2007-05-15 15:29 ` Paul E. McKenney
2007-05-15 16:17 ` Peter Zijlstra
2007-05-15 18:52 ` Paul E. McKenney
2007-05-11 13:15 ` [PATCH 2/2] mm: change mmap_sem over to the " Peter Zijlstra
2007-05-11 16:17 ` Andrew Morton
2007-05-11 17:12 ` Peter Zijlstra
2007-05-11 18:08 ` Andrew Morton
2007-05-14 11:54 ` Nick Piggin
2007-05-11 15:56 ` [PATCH 0/2] convert mmap_sem to a " Ingo Molnar
2007-05-11 16:52 ` Eric Dumazet
2007-05-11 17:18 ` Peter Zijlstra
2007-05-14 12:07 ` Nick Piggin [this message]
2007-05-14 12:57 ` Peter Zijlstra
2007-05-11 17:08 ` Christoph Lameter
2007-05-14 11:58 ` Nick Piggin
2007-05-14 12:38 ` Peter Zijlstra
2007-05-12 9:27 ` Esben Nielsen
2007-05-12 10:01 ` Peter Zijlstra
2007-05-12 13:44 ` Esben Nielsen
2007-05-12 14:33 ` Ingo Molnar
2007-05-12 15:34 ` Esben Nielsen
2007-05-12 15:42 ` Ingo Molnar
2007-05-12 15:26 ` Eric Dumazet
2007-05-14 8:50 ` Esben Nielsen
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