linux-kernel - Re: [PATCH 33/35] libata: take advantage of cmwq and remove concurrency limitations

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Message-ID: <4C292308.4050906@pobox.com>
Date:	Mon, 28 Jun 2010 18:32:40 -0400
From:	Jeff Garzik <jgarzik@...ox.com>
To:	Tejun Heo <tj@...nel.org>
CC:	torvalds@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, dhowells@...hat.com,
	arjan@...ux.intel.com, oleg@...hat.com, axboe@...nel.dk,
	fweisbec@...il.com, dwalker@...eaurora.org,
	stefanr@...6.in-berlin.de, florian@...kler.org,
	andi@...stfloor.org, mst@...hat.com, randy.dunlap@...cle.com
Subject: Re: [PATCH 33/35] libata: take advantage of cmwq and remove concurrency
 limitations

On 06/28/2010 05:04 PM, Tejun Heo wrote:
> libata has two concurrency related limitations.
>
> a. ata_wq which is used for polling PIO has single thread per CPU.  If
>     there are multiple devices doing polling PIO on the same CPU, they
>     can't be executed simultaneously.
>
> b. ata_aux_wq which is used for SCSI probing has single thread.  In
>     cases where SCSI probing is stalled for extended period of time
>     which is possible for ATAPI devices, this will stall all probing.
>
> #a is solved by increasing maximum concurrency of ata_wq.  Please note
> that polling PIO might be used under allocation path and thus needs to
> be served by a separate wq with a rescuer.
>
> #b is solved by using the default wq instead and achieving exclusion
> via per-port mutex.
>
> Signed-off-by: Tejun Heo<tj@...nel.org>
> Cc: Jeff Garzik<jgarzik@...ox.com>

Acked-by: Jeff Garzik <jgarzik@...hat.com>


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