linux-kernel - Re: [PATCH 1/9] move blk_iopoll to limit and make it generally available

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Message-ID: <20151114070200.GA27738@lst.de>
Date:	Sat, 14 Nov 2015 08:02:00 +0100
From:	Christoph Hellwig <hch@....de>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	Sagi Grimberg <sagig@....mellanox.co.il>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	Bart Van Assche <bart.vanassche@...disk.com>, axboe@...com,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] move blk_iopoll to limit and make it generally
	available

On Fri, Nov 13, 2015 at 05:23:39PM +0200, Or Gerlitz wrote:
> On Fri, Nov 13, 2015 at 3:46 PM, Christoph Hellwig <hch@....de> wrote:
> > The new name is irq_poll as iopoll is already taken.  Better suggestions
> > welcome.
> 
> Sagi (or Christoph if you can address that),
> 
> @ some pointer over the last 18 months there was a port done at
> mellanox for iser to use blk-iopoll and AFAIR it didn't work well or
> didn't work at all. Can you tell now what was the problem and how did
> you address it at your generalization?

Hi Or,

Sagi mentioned last time he tried a similar approach in iSER he saw
some large latency sparks.  We've seen nothing worse than the original
approach.  The Flash memory summit slide set has some numbers:

http://www.flashmemorysummit.com/English/Collaterals/Proceedings/2015/20150811_FA11_Bandic.pdf

they aren't quite up to date, but the latency distribution hasn't
really changed.
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