linux-kernel - Re: [patch v3 1/3] block: add a non-queueable flush flag

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Date:	Thu, 5 May 2011 10:21:15 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Jeff Garzik <jgarzik@...ox.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"jaxboe@...ionio.com" <jaxboe@...ionio.com>,
	"htejun@...il.com" <htejun@...il.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"djwong@...ibm.com" <djwong@...ibm.com>,
	"sshtylyov@...sta.com" <sshtylyov@...sta.com>
Subject: Re: [patch v3 1/3] block: add a non-queueable flush flag

On Thu, May 05, 2011 at 10:17:39AM +0800, Jeff Garzik wrote:
> On 05/04/2011 09:59 PM, shaohua.li@...el.com wrote:
> > flush request isn't queueable in some drives. Add a flag to let driver
> > notify block layer about this. We can optimize flush performance with the
> > knowledge.
> >
> > Signed-off-by: Shaohua Li<shaohua.li@...el.com>
> > ---
> >   block/blk-settings.c   |    6 ++++++
> >   include/linux/blkdev.h |    7 +++++++
> >   2 files changed, 13 insertions(+)
> 
> hmmm.
> 
> This assumes that flush on new hardware, by default, is queueable.
> 
> I think the sense should be reversed:  don't enable the optimization, 
> unless we know the optimization works.
> 
> That seems safer than always enabling the optimization, unless we know 
> it does not work.  That is not a fail-safe mode of operation.
This assumes flush is queueable by default. but I only enable the optimization
for non-queueable flush. So the optimization is off by default, please see
the second patch.

Thanks,
Shaohua
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