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

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Message-ID: <20130726020928.GL29296@kernel.dk>
Date:	Thu, 25 Jul 2013 20:09:28 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Alexander Gordeev <agordeev@...hat.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Mike Christie <michaelc@...wisc.edu>,
	Tejun Heo <tj@...nel.org>, 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 Thu, Jul 25 2013, Nicholas A. Bellinger wrote:
> On Thu, 2013-07-25 at 12:16 +0200, Alexander Gordeev wrote:
> > On Mon, Jul 22, 2013 at 02:10:36PM -0700, Nicholas A. Bellinger wrote:
> > > Np.  FYI, you'll want to use the latest commit e7827b351 HEAD from
> > > target-pending/scsi-mq, which now has functioning scsi-generic support.
> > 
> > Survives a boot, a kernel build and the build's result :)
> 
> Great.  Thanks for the feedback Alexander!
> 
> So the next step on my end is to enable -mq for ahci, and verify initial
> correctness using QEMU/KVM hardware emulation.
> 
> Btw, I've been looking at enabling the SHT->cmd_size for struct
> ata_queued_cmd descriptor pre-allocation, but AFAICT these descriptors
> are already all pre-allocated by libata and obtained via ata_qc_new() ->
> __ata_qc_from_tag() during ata_scsi_queuecmd().

Might still not be a bad idea to do it:

- Cleans up a driver, getting rid of the need to alloc, maintain, and
  free those structures.

- Should be some cache locality benefits to having it all sequential.

> So that said, with the struct request + struct scsi_cmnd pre-allocations
> already provided by blk-mq -> scsi-mq code, all memory allocations
> should have already been eliminated from I/O fast path.

Nice!

-- 
Jens Axboe

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