linux-kernel - Re: [RFC]block: add flush request at head

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Message-ID: <1303175224.3981.202.camel@sli10-conroe>
Date:	Tue, 19 Apr 2011 09:07:04 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>, "Shi, Alex" <alex.shi@...el.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [RFC]block: add flush request at head

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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