linux-kernel - Re: [PATCH 1/1] cciss: set max scatter gather entries to 32 on P600

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Message-ID: <520CB9C7.30307@redhat.com>
Date:	Thu, 15 Aug 2013 13:21:43 +0200
From:	Tomas Henzl <thenzl@...hat.com>
To:	"Miller, Mike (OS Dev)" <Mike.Miller@...com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	"mikem@...mper.usa.hp.com" <mikem@...mper.usa.hp.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	LKML-scsi <linux-scsi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"bubrown@...hat.com" <bubrown@...hat.com>,
	"scameron@...rdog.cce.hp.com" <scameron@...rdog.cce.hp.com>
Subject: Re: [PATCH 1/1] cciss: set max scatter gather entries to 32 on P600

On 08/14/2013 11:41 PM, Miller, Mike (OS Dev) wrote:
>
> -----Original Message-----
> From: James Bottomley [mailto:James.Bottomley@...senPartnership.com] 
> Sent: Wednesday, August 14, 2013 4:27 PM
> To: Miller, Mike (OS Dev); mikem@...mper.usa.hp.com
> Cc: Andrew Morton; Jens Axboe; LKML-scsi; LKML; thenzl@...hat.com; bubrown@...hat.com; scameron@...rdog.cce.hp.com
> Subject: Re: [PATCH 1/1] cciss: set max scatter gather entries to 32 on P600
>
> On Wed, 2013-08-14 at 15:52 -0500, Mike Miller wrote:
>> Patch 1/1
>>
>> From: Mike Miller <mike.miller@...com>
>>
>> At one time we used to set the maximum number of scatter gather 
>> elements on all Smart Array controllers to 32. At some point in time 
>> the firmware began to write the "appropriate" value for each controller into the config table.
>> The cciss driver would then read that and set h->maxsgentries.
>>
>>         h->maxsgentries = readl(&(h->cfgtable->MaxSGElements);
>>
>> On the P600 that value is 544. Under some workloads a significant 
>> performance reduction may result. This patch forces the P600 to use 
>> only 32 scatter gather elements. Other controllers are not affected.
>>
>> Signed-off-by: Mike Miller <mike.miller@...com>
>> Signed-off-by: Dwight (Bud) Brown <bubrown@...hat.com>
>> Signed-off-by: Tomas Henzl <thenzl@...hat.com>
>> Acked-by: Stephen M. Cameron <steve.cameron@...com>
> I don't quite understand the signoff chain on this patch.  For a one line patch, are you saying it has three authors?

It look a bit funny, but from what I know everybody from that list^ was somehow involved in that issue, debugging..testing, etc,
so seeing the names there is not that bad. But I'm also not the direct author of the patch so feel free to remove my name from the list.

Tomas

>
> James
>
> The patch origin is unknown. I got it from Tomas and Bud who think it may have originated from HP. I cleaned it up, compile tested it, and sent it on. I'll review my procedures for future patches.
>
> -- mikem
>
>
> --
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