Message-ID: <5154AE1E.6000007@redhat.com>
Date: Thu, 28 Mar 2013 16:54:54 -0400
From: Rik van Riel <riel@redhat.com>
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To: Michel Lespinasse <walken@google.com>
CC: Alex Shi <alex.shi@intel.com>, Ingo Molnar <mingo@kernel.org>,
        David Howells <dhowells@redhat.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Thomas Gleixner <tglx@linutronix.de>,
        Yuanhan Liu <yuanhan.liu@linux.intel.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Dave Chinner <david@fromorbit.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 06/13] rwsem: more agressive lock stealing in rwsem_down_write_failed
References: <1363344869-15732-1-git-send-email-walken@google.com> <1363344869-15732-7-git-send-email-walken@google.com>
In-Reply-To: <1363344869-15732-7-git-send-email-walken@google.com>
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On 03/15/2013 06:54 AM, Michel Lespinasse wrote:
> Some small code simplifications can be achieved by doing more agressive
> lock stealing:
>
> - When rwsem_down_write_failed() notices that there are no active locks
>    (and thus no thread to wake us if we decided to sleep), it used to wake
>    the first queued process. However, stealing the lock is also sufficient
>    to deal with this case, so we don't need this check anymore.
>
> - In try_get_writer_sem(), we can steal the lock even when the first waiter
>    is a reader. This is correct because the code path that wakes readers is
>    protected by the wait_lock. As to the performance effects of this change,
>    they are expected to be minimal: readers are still granted the lock
>    (rather than having to acquire it themselves) when they reach the front
>    of the wait queue, so we have essentially the same behavior as in
>    rwsem-spinlock.
>
> Signed-off-by: Michel Lespinasse <walken@google.com>

Reviewed-by: Rik van Riel <riel@redhat.com>

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