linux-kernel - Re: [PATCH v1 7/7] xen-block: implement indirect descriptors

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Message-ID: <20130417172747.GA25736@phenom.dumpdata.com>
Date:	Wed, 17 Apr 2013 13:27:47 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Roger Pau Monné <roger.pau@...rix.com>,
	martin.peterson@...cle.com, axboe@...nel.dk
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v1 7/7] xen-block: implement indirect descriptors

On Wed, Apr 17, 2013 at 07:04:51PM +0200, Roger Pau Monné wrote:
> On 17/04/13 16:25, Konrad Rzeszutek Wilk wrote:
> >>> Perhaps the xen-blkfront part of the patch should be just split out to make
> >>> this easier?
> >>>
> >>> Perhaps what we really should have is just the 'max' value of megabytes
> >>> we want to handle on the ring.
> >>>
> >>> As right now 32 ring requests * 32 segments = 4MB.  But if the user wants
> >>> to se the max: 32 * 4096 = so 512MB (right? each request would handle now 16MB
> >>> and since we have 32 of them = 512MB).
> >>
> >> I've just set that to something that brings a performance benefit
> >> without having to map an insane number of persistent grants in blkback.
> >>
> >> Yes, the values are correct, but the device request queue (rq) is only
> >> able to provide read requests with 64 segments or write requests with
> >> 128 segments. I haven't been able to get larger requests, even when
> >> setting this to 512 or higer.
> > 
> > What are you using to drive the requests? 'fio'?
> 
> Yes, I've tried fio with several "bs=" values, but it doesn't seem to
> change the size of the underlying requests. Have you been able to get
> bigger requests?

Martin, Jens,
Any way to drive more than 128 segments?
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