From: Tejun Heo <tj@kernel.org>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Roman Pen <roman.penyaev@profitbricks.com>,
Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 1/1] [RFC] workqueue: fix ghost PENDING flag while doing MQ IO
Date: Tue, 26 Apr 2016 13:45:13 -0400 [thread overview]
Message-ID: <20160426174513.GM7822@mtj.duckdns.org> (raw)
In-Reply-To: <571FA51F.2040702@hurleysoftware.com>
Hello, Peter.
On Tue, Apr 26, 2016 at 10:27:59AM -0700, Peter Hurley wrote:
> > It's unlikely to make any measureable difference. Is xchg() actually
> > cheaper than store + rmb?
>
> store + mfence (full barrier), yes. Roughly 2x faster.
>
> https://lkml.org/lkml/2015/11/2/607
Ah, didn't know that. Thanks for the pointer.
> > I'm not necessarily against making all clearings of
> > PENDING to be followed by a rmb or use xhcg. Reasons 2-4 are pretty
> > weak tho.
>
> I agree 2 and 3 are not the best reasons.
> Actually, it looks that I'm in the minority anyway, and that style-wise,
> naked barrier is preferred.
As long as what's happening is clearly documented, I think either is
fine. I'm gonna go with Roman's mb patch for -stable fix but think
it'd be nice to have a separate patch to consolidate the paths which
clear PENDING and make them use xchg. If you can spin up a patch for
that, I'd be happy to apply it to wq/for-3.7.
Thanks.
--
tejun
next prev parent reply other threads:[~2016-04-26 17:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-25 15:22 [PATCH 1/1] [RFC] workqueue: fix ghost PENDING flag while doing MQ IO Roman Pen
2016-04-25 15:48 ` Tejun Heo
2016-04-25 16:00 ` Tejun Heo
2016-04-25 16:40 ` Roman Penyaev
2016-04-25 16:34 ` Roman Penyaev
2016-04-25 17:03 ` Tejun Heo
2016-04-25 17:39 ` Roman Penyaev
2016-04-25 17:51 ` Tejun Heo
2016-04-26 1:22 ` Peter Hurley
2016-04-26 15:15 ` Tejun Heo
2016-04-26 17:27 ` Peter Hurley
2016-04-26 17:45 ` Tejun Heo [this message]
2016-04-26 20:07 ` Peter Hurley
2016-04-27 5:50 ` Hannes Reinecke
2016-04-27 19:05 ` Tejun Heo
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