Re: [PATCH libata/for-3.16-fixes] libata: introduce ata_host->n_tags to avoid oops on SAS controllers

[Tejun Heo]

Hello,

On Wed, Jul 23, 2014 at 06:46:05PM +0200, Bartlomiej Zolnierkiewicz wrote:
> On Wednesday, July 23, 2014 12:36:01 PM Tejun Heo wrote:
> BTW:
> 		/* the last tag is reserved for internal command. */
> 		if (tag == ATA_TAG_INTERNAL)
> 			continue;
> 
> in ata_qc_new()'s loop now becomes a dead code (loop will be done
> maximum ATA_MAX_QUEUE - 2 times and ATA_TAG_INTERNAL is defined
> as ATA_MAX_QUEUE - 1).  Compiler can probably optimize it away so
> as a bonus of your patch we may get one condition check less in
> a hot-path. :)

ATA_TAG_INTERNAL will soon be replaced by a qc flag so this should all
go away pretty soon.  ata_qc_new() is quite badly implemented tho.  It
has no reason to do atomic test_and_set_bit() and there are far more
efficient ways to implement what it does.  If anybody is interested in
improving it, please go ahead.

Thanks.

-- 
tejun
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