linux-kernel - Re: [PATCH] scsi: megaraid_sas - throttle io if cmds are in risk of being timed-out

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Message-Id: <1174083775.3519.54.camel@mulgrave.il.steeleye.com>
Date:	Fri, 16 Mar 2007 17:22:55 -0500
From:	James Bottomley <James.Bottomley@...elEye.com>
To:	Sumant Patro <sumant.patro@....com>
Cc:	akpm@...l.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, neela.kolli@....com, bo.yang@....com
Subject: Re: [PATCH] scsi: megaraid_sas - throttle io if cmds are in risk
	of being timed-out

On Thu, 2007-03-01 at 13:29 -0800, Sumant Patro wrote:
> Driver to throttle IO to reduce risk of OS timing out cmds.
> 
> Implemented a circular queue to keep track of pending OS cmds in FW. 
> This queue is periodically (every 10 sec) checked by a timer routine.
> If there is any cmd that is in risk of getting timed-out by the OS, 
> the host->can_queue is reduced to 16 and MEGASAS_FW_BUSY flag is set. 
> The host->can_queue will be restored to default value when the following 
> two conditions are met : 5 secs has elapsed and the # of outstanding cmds
> in FW is less than 17.
> Also increased the per cmd timeout to 120*HZ from 90*HZ.

OK, this is still not nice.  What you need to be doing is intercepting
the timeout before it fires (and quiesces the machine).  Currently the
eh_timed_out() callback is only exposed to transport classes, I'll put
it back into the host template and then you can use it.

James


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