From: Peter Zijlstra <peterz@infradead.org>
To: rajman mekaco <rajman.mekaco@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Andrew Morton <akpm@linux-foundation.org>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Minchan Kim <minchan.kim@gmail.com>,
Christoph Lameter <cl@gentwo.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user_struct spinlock
Date: Thu, 03 May 2012 21:31:14 +0200 [thread overview]
Message-ID: <1336073474.6509.2.camel@twins> (raw)
In-Reply-To: <1336066477-3964-1-git-send-email-rajman.mekaco@gmail.com>
On Thu, 2012-05-03 at 23:04 +0530, rajman mekaco wrote:
> The user_shm_lock and user_shm_unlock functions use a single global
> spinlock for protecting the user->locked_shm.
Are you very sure its only protecting user state? This changelog doesn't
convince me you've gone through everything and found it good.
> This is an overhead for multiple CPUs calling this code even if they
> are having different user_struct.
>
> Remove the global shmlock_user_lock and introduce and use a new
> spinlock inside of the user_struct structure.
While I don't immediately see anything wrong with it, I doubt its
useful. What workload run with enough users that this makes a difference
one way or another?
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: rajman mekaco <rajman.mekaco@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Andrew Morton <akpm@linux-foundation.org>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Minchan Kim <minchan.kim@gmail.com>,
Christoph Lameter <cl@gentwo.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user_struct spinlock
Date: Thu, 03 May 2012 21:31:14 +0200 [thread overview]
Message-ID: <1336073474.6509.2.camel@twins> (raw)
In-Reply-To: <1336066477-3964-1-git-send-email-rajman.mekaco@gmail.com>
On Thu, 2012-05-03 at 23:04 +0530, rajman mekaco wrote:
> The user_shm_lock and user_shm_unlock functions use a single global
> spinlock for protecting the user->locked_shm.
Are you very sure its only protecting user state? This changelog doesn't
convince me you've gone through everything and found it good.
> This is an overhead for multiple CPUs calling this code even if they
> are having different user_struct.
>
> Remove the global shmlock_user_lock and introduce and use a new
> spinlock inside of the user_struct structure.
While I don't immediately see anything wrong with it, I doubt its
useful. What workload run with enough users that this makes a difference
one way or another?
next prev parent reply other threads:[~2012-05-03 19:31 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-03 17:34 [PATCH 1/1] mlock: split the shmlock_user_lock spinlock into per user_struct spinlock rajman mekaco
2012-05-03 17:34 ` rajman mekaco
2012-05-03 18:07 ` Rik van Riel
2012-05-03 18:07 ` Rik van Riel
2012-05-03 20:27 ` Rik van Riel
2012-05-03 20:27 ` Rik van Riel
2012-05-04 1:12 ` rajman mekaco
2012-05-04 1:12 ` rajman mekaco
2012-05-10 13:34 ` rajman mekaco
2012-05-10 13:34 ` rajman mekaco
2012-05-10 14:54 ` Rik van Riel
2012-05-10 14:54 ` Rik van Riel
2012-05-10 15:39 ` rajman mekaco
2012-05-10 15:39 ` rajman mekaco
2012-05-10 16:48 ` rajman mekaco
2012-05-10 16:48 ` rajman mekaco
2012-05-10 22:30 ` Rik van Riel
2012-05-10 22:30 ` Rik van Riel
2012-05-12 3:10 ` rajman mekaco
2012-05-12 3:10 ` rajman mekaco
2012-05-03 19:31 ` Peter Zijlstra [this message]
2012-05-03 19:31 ` Peter Zijlstra
2012-05-03 20:26 ` Rik van Riel
2012-05-03 20:26 ` Rik van Riel
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