linux-kernel - Re: [PATCH v3 66/77] ncr5380: Fix soft lockups

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Message-ID: <567903EA.7030803@suse.de>
Date:	Tue, 22 Dec 2015 09:03:54 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Finn Thain <fthain@...egraphics.com.au>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Michael Schmitz <schmitzmic@...il.com>,
	linux-m68k@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 66/77] ncr5380: Fix soft lockups

On 12/22/2015 02:18 AM, Finn Thain wrote:
> Because of the rudimentary design of the chip, it is necessary to poll the
> SCSI bus signals during PIO and this tends to hog the CPU. The driver will
> accept new commands while others execute, and this causes a soft lockup
> because the workqueue item will not terminate until the issue queue is
> emptied.
>
> When exercising dmx3191d using sequential IO from dd, the driver is sent
> 512 KiB WRITE commands and 128 KiB READs. For a PIO transfer, the rate is
> is only about 300 KiB/s, so these are long-running commands. And although
> PDMA may run at several MiB/s, interrupts are disabled for the duration
> of the transfer.
>
> Fix the unresponsiveness and soft lockup issues by calling cond_resched()
> after each command is completed and by limiting max_sectors for drivers
> that don't implement real DMA.
>
> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
>
> ---
>
> Changed since v2:
> - Moved max_sectors initialization to wrapper drivers. It isn't really
>    relevant to the core driver and compile-time configuration using macros
>    like REAL_DMA should be avoided.
>
> ---
>   drivers/scsi/NCR5380.c       |    6 ++++--
>   drivers/scsi/arm/cumana_1.c  |    1 +
>   drivers/scsi/arm/oak.c       |    1 +
>   drivers/scsi/atari_NCR5380.c |    6 ++++--
>   drivers/scsi/dmx3191d.c      |    1 +
>   drivers/scsi/dtc.c           |    1 +
>   drivers/scsi/g_NCR5380.c     |    1 +
>   drivers/scsi/mac_scsi.c      |    1 +
>   drivers/scsi/pas16.c         |    1 +
>   drivers/scsi/t128.c          |    1 +
>   10 files changed, 16 insertions(+), 4 deletions(-)
>
Reviewed-by: Hannes Reinecke <hare@...e.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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