linux-kernel - Re: absurdly high "optimal_io

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Date:	Thu, 06 Nov 2014 11:15:32 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Chris Friesen <chris.friesen@...driver.com>
CC:	lkml <linux-kernel@...r.kernel.org>, linux-scsi@...r.kernel.org,
	Mike Snitzer <snitzer@...hat.com>
Subject: Re: absurdly high "optimal_io_size" on Seagate SAS disk

On 2014-11-06 11:12, Martin K. Petersen wrote:
>>>>>> "Chris" == Chris Friesen <chris.friesen@...driver.com> writes:
>
> Chris> That'd work, but is it the best way to go?  I mean, I found one
> Chris> report of a similar problem on an SSD (model number unknown).  In
> Chris> that case it was a near-UINT_MAX value as well.
>
> My concern is still the same. Namely that this particular drive happens
> to be returning UINT_MAX but it might as well be a value that's entirely
> random. Or even a value that is small and innocuous looking but
> completely wrong.
>
> Chris> The problem with the blacklist is that until someone patches it,
> Chris> the drive is broken.  And then it stays blacklisted even if the
> Chris> firmware gets fixed.
>
> Well, you can manually blacklist in /proc/scsi/device_info.
>
> Chris> I'm wondering if it might not be better to just ignore all values
> Chris> larger than X (where X is whatever we think is the largest
> Chris> conceivable reasonable value).
>
> The problem is that finding that is not easy and it too will be a moving
> target.

Didn't check, but assuming the value is the upper 24 bits of 32. If so, 
might not hurt to check for as 0xfffffe00 as an invalid value.

-- 
Jens Axboe

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