From: David Howells <dhowells@redhat.com>
To: Michel Lespinasse <walken@google.com>
Cc: dhowells@redhat.com, Andrew Morton <akpm@google.com>,
Linux-MM <linux-mm@kvack.org>, Ying Han <yinghan@google.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: rwsem: down_read_unfair() proposal
Date: Wed, 05 May 2010 11:06:44 +0100 [thread overview]
Message-ID: <22994.1273054004@redhat.com> (raw)
In-Reply-To: <20100505032033.GA19232@google.com>
Michel Lespinasse <walken@google.com> wrote:
> and looks like it's doable with the x86 rwsem implementation as well in a
> way that would only involve changes to the rwsem spinlock-protected slow
> paths in lib/rwsem.c .
It's not as easy as it seems. Once an XADD-based rwsem is contended, you
cannot necessarily tell without looking at the queue whether the rwsem is
currently write-locked or read-locked.
David
WARNING: multiple messages have this Message-ID (diff)
From: David Howells <dhowells@redhat.com>
To: Michel Lespinasse <walken@google.com>
Cc: dhowells@redhat.com, Andrew Morton <akpm@google.com>,
Linux-MM <linux-mm@kvack.org>, Ying Han <yinghan@google.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: rwsem: down_read_unfair() proposal
Date: Wed, 05 May 2010 11:06:44 +0100 [thread overview]
Message-ID: <22994.1273054004@redhat.com> (raw)
In-Reply-To: <20100505032033.GA19232@google.com>
Michel Lespinasse <walken@google.com> wrote:
> and looks like it's doable with the x86 rwsem implementation as well in a
> way that would only involve changes to the rwsem spinlock-protected slow
> paths in lib/rwsem.c .
It's not as easy as it seems. Once an XADD-based rwsem is contended, you
cannot necessarily tell without looking at the queue whether the rwsem is
currently write-locked or read-locked.
David
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next prev parent reply other threads:[~2010-05-05 10:06 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-05 3:20 rwsem: down_read_unfair() proposal Michel Lespinasse
2010-05-05 3:20 ` Michel Lespinasse
2010-05-05 10:03 ` David Howells
2010-05-05 10:03 ` David Howells
2010-05-05 10:36 ` Michel Lespinasse
2010-05-05 10:36 ` Michel Lespinasse
2010-05-06 23:26 ` Mike Waychison
2010-05-06 23:26 ` Mike Waychison
2010-05-05 10:06 ` David Howells [this message]
2010-05-05 10:06 ` David Howells
2010-05-05 10:48 ` Michel Lespinasse
2010-05-05 10:48 ` Michel Lespinasse
2010-05-05 11:09 ` David Howells
2010-05-05 11:09 ` David Howells
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