linux-kernel - Re: [PATCH v3] storvsc: use small sg

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Message-Id: <1465493159.2259.14.camel@linux.vnet.ibm.com>
Date:	Thu, 09 Jun 2016 10:25:59 -0700
From:	James Bottomley <jejb@...ux.vnet.ibm.com>
To:	Olaf Hering <olaf@...fle.de>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH v3] storvsc: use small sg_tablesize on x86

On Thu, 2016-06-09 at 18:25 +0200, Olaf Hering wrote:
> Reducing the sg_tablesize allows booting of 32bit kernels in VMs,
> after
> commit be0cf6ca301c61458dc4aa1a37acf4f58d2ed3d6 ("scsi: storvsc: Set
> the
> tablesize based on the information given by the host")
> 
> [    5.567138] hv_storvsc vmbus_1: adjusting sg_tablesize 0x800 -> 
> 0x20

Are you really sure 32 is the correct size?  That caps transfers at 128
k.  Even in the dim, dark, pre-64bit (at least on x86) days, our static
limit for sg tablesize was 128 (0.5M).

I know 32 it what it had before, but the reason for the commit you
quote was to improve performance ...

James