Subject: Re: [RFC]block: add flush request at head
From: Shaohua Li <shaohua.li@intel.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <jaxboe@fusionio.com>, lkml <linux-kernel@vger.kernel.org>,
        Tejun Heo <htejun@gmail.com>, "Shi, Alex" <alex.shi@intel.com>,
        "Chen, Tim C" <tim.c.chen@intel.com>
In-Reply-To: <20110418092607.GA3837@infradead.org>
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	 <4DABF194.4010603@fusionio.com>  <20110418092607.GA3837@infradead.org>
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Date: Tue, 19 Apr 2011 09:07:04 +0800
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On Mon, 2011-04-18 at 17:26 +0800, Christoph Hellwig wrote:
> On Mon, Apr 18, 2011 at 10:08:52AM +0200, Jens Axboe wrote:
> > Might be worth adding something for this special case, seems like the
> > NCQ restrictions will continue to be around forever (or a long time, at
> > least).
> 
> I heared people are working on adding a queued FLUSH to the standard,
> but it's going to take a long time for it to get into real life systems.
> 
> What would help now is allowing libata to actually use the FUA bit,
> given that every common disk and controller supports it these days.
> 
> Shaohua, does adding a
> 
> 	libata.fua = 1
> 
> to the kernel command line help your benchmark in any way?  It should
> if you flushes are mostly from journal writes, but not from fsync
> that didn't change any metadata.
This is a workload with fsync. I tested libata.fua=1, but nothing changed.

I also hacked the code when we proceed queue running flush list, also
proceed queue pending flush list, which doesn't change correctness for
sata. This improved a little, around 5%, but doesn't recover the whole
regression. so I still need add the flush request at queue head.

Thanks,
Shaohua


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