From: Tim Chen <tim.c.chen@linux.intel.com>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>,
Alex Shi <alex.shi@intel.com>,
Michel Lespinasse <walken@google.com>,
Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Andi Kleen <andi@firstfloor.org>,
Matthew R Wilcox <matthew.r.wilcox@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH 2/2] rwsem: do optimistic spinning for writer lock acquisition
Date: Mon, 24 Jun 2013 14:30:38 -0700 [thread overview]
Message-ID: <1372109438.22432.75.camel@schen9-DESK> (raw)
In-Reply-To: <51C8B0AA.4070204@hurleysoftware.com>
On Mon, 2013-06-24 at 16:48 -0400, Peter Hurley wrote:
>
> Also, I haven't given a lot of thought to if preemption must be disabled
> before calling rwsem_can_spin_on_owner(). If so, wouldn't you just drop
> rwsem_can_spin_on_owner() (because the conditions tested in the loop are
> equivalent)?
>
Not totally equivalent. If we drop the call to rwsem_can_spin_on_owner,
we will spin when readers are holding the lock (owner is null).
Right now we only allow writers to spin when other writers are
holding the lock by adding the rwsem_can_spin_on_owner check.
Letting spinning on readers held lock is tricky as
we could have a reader that sleeps and if we don't detect the case. We
could spin for too long.
Thanks.
Tim
next prev parent reply other threads:[~2013-06-24 21:30 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1371855277.git.tim.c.chen@linux.intel.com>
2013-06-21 23:51 ` [PATCH 1/2] rwsem: check the lock before cpmxchg in down_write_trylock and rwsem_do_wake Tim Chen
2013-06-22 0:10 ` Alex Shi
2013-06-22 0:15 ` Davidlohr Bueso
2013-06-24 16:34 ` Tim Chen
2013-06-22 7:21 ` Peter Hurley
2013-06-23 1:16 ` Alex Shi
2013-06-23 5:10 ` Andi Kleen
2013-06-23 11:52 ` Alex Shi
2013-06-21 23:51 ` [PATCH 2/2] rwsem: do optimistic spinning for writer lock acquisition Tim Chen
2013-06-22 0:00 ` Davidlohr Bueso
2013-06-22 7:57 ` Peter Hurley
2013-06-23 20:03 ` Davidlohr Bueso
2013-06-24 17:11 ` Tim Chen
2013-06-24 18:49 ` Peter Hurley
2013-06-24 19:13 ` Tim Chen
2013-06-24 20:32 ` Peter Hurley
2013-06-24 20:17 ` Tim Chen
2013-06-24 20:48 ` Peter Hurley
2013-06-24 21:30 ` Tim Chen [this message]
2013-06-25 7:37 ` Peter Zijlstra
2013-06-25 16:00 ` Tim Chen
2013-06-24 21:58 ` Tim Chen
2013-06-24 22:08 ` Peter Hurley
2013-06-24 8:46 ` Peter Zijlstra
2013-06-24 16:36 ` Tim Chen
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