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From: Waiman Long <waiman.long@hpe.com>
To: Davidlohr Bueso <dave@stgolabs.net>
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>
Subject: Re: [RFC PATCH-tip 2/6] locking/rwsem: Enable optional count-based spinning on reader
Date: Tue, 14 Jun 2016 15:11:23 -0400	[thread overview]
Message-ID: <576056DB.5050701@hpe.com> (raw)
In-Reply-To: <20160614182757.GA15903@linux-80c1.suse>

On 06/14/2016 02:27 PM, Davidlohr Bueso wrote:
> 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

I understand your concern. I will see if there is a way to autotune 
instead of using explicit enablement.

Cheers,
Longman

  reply	other threads:[~2016-06-14 19:26 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-14 18:12 [RFC PATCH-tip 0/6] locking/rwsem: Enable reader optimistic spinning Waiman Long
2016-06-14 18:12 ` [RFC PATCH-tip 1/6] locking/rwsem: Stop active read lock ASAP Waiman Long
2016-06-14 18:12 ` [RFC PATCH-tip 2/6] locking/rwsem: Enable optional count-based spinning on reader Waiman Long
2016-06-14 18:27   ` Davidlohr Bueso
2016-06-14 19:11     ` Waiman Long [this message]
2016-06-14 18:12 ` [RFC PATCH-tip 3/6] locking/rwsem: move down rwsem_down_read_failed function Waiman Long
2016-06-14 18:12 ` [RFC PATCH-tip 4/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation Waiman Long
2016-06-14 18:12 ` [RFC PATCH-tip 5/6] locking/rwsem: Enable spinning readers Waiman Long
2016-06-14 18:12 ` [RFC PATCH-tip 6/6] xfs: Enable reader optimistic spinning for DAX inodes Waiman Long
2016-06-14 18:24   ` Christoph Hellwig
2016-06-14 19:08     ` Waiman Long
2016-06-14 23:06   ` Dave Chinner
2016-06-15 18:55     ` Waiman Long

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