From mboxrd@z Thu Jan  1 00:00:00 1970
From: Davidlohr Bueso <dave@stgolabs.net>
Date: Tue, 14 Jun 2016 18:27:57 +0000
Subject: Re: [RFC PATCH-tip 2/6] locking/rwsem: Enable optional count-based spinning on reader
Message-Id: <20160614182757.GA15903@linux-80c1.suse>
List-Id: <linux-ia64.vger.kernel.org>
References: <1465927959-39719-1-git-send-email-Waiman.Long@hpe.com>
 <1465927959-39719-3-git-send-email-Waiman.Long@hpe.com>
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To: Waiman Long <Waiman.Long@hpe.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, xfs@oss.sgi.com, Jason Low <jason.low2@hp.com>, Dave Chinner <david@fromorbit.com>, Scott J Norton <scott.norton@hpe.com>, Douglas Hatch <doug.hatch@hpe.com>

On Tue, 14 Jun 2016, Waiman Long wrote:

>This patch provides a way for the kernel code to designate specific
>rwsems to be more aggressive in term of optimistic spinning that the
>writers will continue to spin for some additional count-based time to
>see if it can get the lock before sleeping. This aggressive spinning
>mode should only be used on rwsems where the readers are unlikely to
>go to sleep.

Yikes, exposing this sort of thing makes me _very_ uneasy, not to mention
the ad-hoc nature and its easiness to mess up. I'm not really for this, even
if it shows extraordinary performance boosts on benchmarks.

Thanks,
Davidlohr