linux-kernel - RE: [PATCH] scsi: megaraid_sas - throttle io if cmds are in riskof being timed-out

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Date:	Mon, 19 Mar 2007 17:08:54 -0600
From:	"Patro, Sumant" <Sumant.Patro@....com>
To:	"James Bottomley" <James.Bottomley@...elEye.com>
Cc:	<akpm@...l.org>, <linux-scsi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	"Kolli, Neela" <Neela.Kolli@....com>, "Yang, Bo" <Bo.Yang@....com>
Subject: RE: [PATCH] scsi: megaraid_sas - throttle io if cmds are in riskof being timed-out


Thank you James.
I will submit new patch that will throttle (if required) from
eh_timed_out call back.

Regards,

Sumant


-----Original Message-----
From: James Bottomley [mailto:James.Bottomley@...elEye.com] 
Sent: Friday, March 16, 2007 3:23 PM
To: Patro, Sumant
Cc: akpm@...l.org; linux-scsi@...r.kernel.org;
linux-kernel@...r.kernel.org; Kolli, Neela; Yang, Bo
Subject: Re: [PATCH] scsi: megaraid_sas - throttle io if cmds are in
riskof 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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