From: Hannes Reinecke <hare@suse.de>
To: Tejun Heo <tj@kernel.org>, 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: Wed, 27 Apr 2016 07:50:01 +0200 [thread overview]
Message-ID: <57205309.2060708@suse.de> (raw)
In-Reply-To: <20160426174513.GM7822@mtj.duckdns.org>
On 04/26/2016 07:45 PM, Tejun Heo wrote:
> 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.
> ^^^
Ah. Time warp.
I knew it would happen eventually :-)
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@suse.de +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
next prev parent reply other threads:[~2016-04-27 5:50 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
2016-04-26 20:07 ` Peter Hurley
2016-04-27 5:50 ` Hannes Reinecke [this message]
2016-04-27 19:05 ` Tejun Heo
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