Re: [PATCH 33/35] libata: take advantage of cmwq and remove concurrencylimitations

[Jeff Garzik]

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@xxxxxxxxxx>
> Cc: Jeff Garzik<jgarzik@xxxxxxxxx>

Acked-by: Jeff Garzik <jgarzik@xxxxxxxxxx>


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