linux-kernel - Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

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Date:	Mon, 29 Jul 2013 08:03:25 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Tejun Heo <tj@...nel.org>
CC:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Alexander Gordeev <agordeev@...hat.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Mike Christie <michaelc@...wisc.edu>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	Jeff Garzik <jgarzik@...ox.com>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

On 07/29/2013 05:46 AM, Tejun Heo wrote:
> Hello,
> 
> On Fri, Jul 26, 2013 at 02:14:36PM -0700, Nicholas A. Bellinger wrote:
>> So I don't think (completely) getting rid of ata_port->qcmds[] will be
>> possible, and just converting the ata_scsi_queuecmd() path to use the
>> extra SHT->cmd_size pre-allocation for *ata_queued_cmd might end up
>> being more trouble that it's worth.  Still undecided on that part..
>>
>> Tejun, do you have any thoughts + input here..?
> 
> libata exception handling which includes probing doesn't go through
> SCSI at all.  It all works inside libata proper using ata_queuecmds
> and only the result is exposed to SCSI.  Most of those SCSI semantics
> need to be emulated anyway, so this makes things a lot easier than
> going through SCSI for each command.  As it currently stands, it'd be
> a lot of effort to try to embed ata_qc's into higher layer construct.
> Given how it's used, I don't think it's a high priority task.
> 
> One thing which would probably be worthwhile tho is getting rid of the
> bitmap based qc tag allocator in libata.  That one is just borderline
> stupid to keep around on any setup which is supposed to be scalable.

Your border might be wider than mine :-). Yes, the bitmap should
definitely go.

-- 
Jens Axboe

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