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From: Peter Zijlstra <peterz@infradead.org>
To: Michel Lespinasse <walken@google.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>,
	Nick Piggin <npiggin@kernel.dk>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 6/6] x86 rwsem: more precise rwsem_is_contended() implementation
Date: Fri, 03 Dec 2010 23:41:10 +0100	[thread overview]
Message-ID: <1291416070.2032.92.camel@laptop> (raw)
In-Reply-To: <1291335412-16231-7-git-send-email-walken@google.com>

On Thu, 2010-12-02 at 16:16 -0800, Michel Lespinasse wrote:
> We would like rwsem_is_contended() to return true only once a contending
> writer has had a chance to insert itself onto the rwsem wait queue.
> To that end, we need to differenciate between active and queued writers.

So you're only considering writer-writer contention? Not writer-reader
and reader-writer contention?

I'd argue rwsem_is_contended() should return true if there is _any_
blocked task, be it a read or a writer.

If you want something else call it something else, like
rwsem_is_write_contended() (there's a pending writer), or
rwsem_is_read_contended() (there's a pending reader).



WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Michel Lespinasse <walken@google.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>,
	Nick Piggin <npiggin@kernel.dk>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 6/6] x86 rwsem: more precise rwsem_is_contended() implementation
Date: Fri, 03 Dec 2010 23:41:10 +0100	[thread overview]
Message-ID: <1291416070.2032.92.camel@laptop> (raw)
In-Reply-To: <1291335412-16231-7-git-send-email-walken@google.com>

On Thu, 2010-12-02 at 16:16 -0800, Michel Lespinasse wrote:
> We would like rwsem_is_contended() to return true only once a contending
> writer has had a chance to insert itself onto the rwsem wait queue.
> To that end, we need to differenciate between active and queued writers.

So you're only considering writer-writer contention? Not writer-reader
and reader-writer contention?

I'd argue rwsem_is_contended() should return true if there is _any_
blocked task, be it a read or a writer.

If you want something else call it something else, like
rwsem_is_write_contended() (there's a pending writer), or
rwsem_is_read_contended() (there's a pending reader).


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  reply	other threads:[~2010-12-03 22:40 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-12-03  0:16 [PATCH 0/6] mlock: do not hold mmap_sem for extended periods of time Michel Lespinasse
2010-12-03  0:16 ` Michel Lespinasse
2010-12-03  0:16 ` [PATCH 1/6] mlock: only hold mmap_sem in shared mode when faulting in pages Michel Lespinasse
2010-12-03  0:16   ` Michel Lespinasse
2010-12-08 23:27   ` Andrew Morton
2010-12-08 23:27     ` Andrew Morton
2010-12-08 23:58     ` Michel Lespinasse
2010-12-08 23:58       ` Michel Lespinasse
2010-12-10  6:11       ` Linus Torvalds
2010-12-10  6:11         ` Linus Torvalds
2010-12-10  6:39         ` Michel Lespinasse
2010-12-10  6:39           ` Michel Lespinasse
2010-12-10 11:12           ` Peter Zijlstra
2010-12-10 11:12             ` Peter Zijlstra
2010-12-14  0:51         ` Michel Lespinasse
2010-12-14  0:51           ` Michel Lespinasse
2010-12-14  1:05           ` Andrew Morton
2010-12-14  1:05             ` Andrew Morton
2010-12-14  1:26             ` Michel Lespinasse
2010-12-14  1:26               ` Michel Lespinasse
2010-12-14 15:43             ` Linus Torvalds
2010-12-14 15:43               ` Linus Torvalds
2010-12-14 23:22               ` Michel Lespinasse
2010-12-14 23:22                 ` Michel Lespinasse
2010-12-03  0:16 ` [PATCH 2/6] mm: add FOLL_MLOCK follow_page flag Michel Lespinasse
2010-12-03  0:16   ` Michel Lespinasse
2010-12-04  6:55   ` Michel Lespinasse
2010-12-04  6:55     ` Michel Lespinasse
2010-12-03  0:16 ` [PATCH 3/6] mm: move VM_LOCKED check to __mlock_vma_pages_range() Michel Lespinasse
2010-12-03  0:16   ` Michel Lespinasse
2010-12-03  0:16 ` [PATCH 4/6] rwsem: implement rwsem_is_contended() Michel Lespinasse
2010-12-03  0:16   ` Michel Lespinasse
2010-12-03  0:16 ` [PATCH 5/6] mlock: do not hold mmap_sem for extended periods of time Michel Lespinasse
2010-12-03  0:16   ` Michel Lespinasse
2010-12-08 23:42   ` Andrew Morton
2010-12-08 23:42     ` Andrew Morton
2010-12-03  0:16 ` [PATCH 6/6] x86 rwsem: more precise rwsem_is_contended() implementation Michel Lespinasse
2010-12-03  0:16   ` Michel Lespinasse
2010-12-03 22:41   ` Peter Zijlstra [this message]
2010-12-03 22:41     ` Peter Zijlstra
2010-12-03 22:51     ` Michel Lespinasse
2010-12-03 22:51       ` Michel Lespinasse
2010-12-03 23:02 ` [PATCH 0/6] mlock: do not hold mmap_sem for extended periods of time Michel Lespinasse
2010-12-03 23:02   ` Michel Lespinasse

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