linux-kernel - Re: [PATCH 11/12] libata: use IRQ expecting

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Date:	Tue, 27 Jul 2010 13:37:45 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Tejun Heo <tj@...nel.org>
CC:	mingo@...e.hu, tglx@...utronix.de, bphilips@...e.de,
	yinghai@...nel.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, stern@...land.harvard.edu,
	gregkh@...e.de, khali@...ux-fr.org
Subject: Re: [PATCH 11/12] libata: use IRQ expecting

On 07/02/2010 10:41 AM, Tejun Heo wrote:
> Hello, Jeff.
>
> So, something like the following.  This should be applied on top of
> the two previous libata patches.  The amount of code in the hot path
> is very small.  Compared to the cpu actually taking an interrupt and
> accessing hardware, it should be negligible, and this will give us
> working and acceptably performing systems in the presence of most
> types of IRQ problems.
>
> Thanks.
>
> Subject: [PATCH] libata: use IRQ expecting
>
> Legacy ATA is very susceptible to IRQ delivery problems in both
> directions - lost and spurious interrupts.  In traditional PATA, the
> IRQ line is ultimately out of the controller and driver's control.
>
> Even relatively new SATA controllers share this problem as many still
> emulate the traditional IDE interface which doesn't have reliable way
> to indicate interrupt pending state and there also is an issue
> regarding the interpretation of nIEN on both sides of the cable.
>
> Controllers with native interface have fewer problems compared to the
> ones which use SFF but they still are affected by IRQ misrouting or
> broken MSI implementations.
>
> IRQ delivery problems on ATA are particularly nasty because it
> commonly hosts installation and/or booting.
>
> Most of these problems can be worked around by using the new IRQ
> expecting mechanism without adding any noticeable overhead.  In ATA,
> almost all operations are initiated by the host and the controller
> signals progress or completion using IRQ.  IRQ expecting can easily be
> added in libata core and applied to all libata drivers.
>
> Signed-off-by: Tejun Heo<tj@...nel.org>
> ---
>   drivers/ata/libata-core.c |   55 ++++++++++++++++++++++++++++++----------------
>   drivers/ata/libata-eh.c   |    4 ++-
>   drivers/ata/libata-sff.c  |   37 +++++++++++++++---------------
>   include/linux/libata.h    |    2 +
>   4 files changed, 60 insertions(+), 38 deletions(-)

I suppose the few cycles it costs are worth it...

Assuming this new version (from July 2) is tested,

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


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