linux-kernel - Re: absurdly high "optimal_io

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Message-ID: <yq1fvdwb3lq.fsf@sermon.lab.mkp.net>
Date:	Thu, 06 Nov 2014 13:12:17 -0500
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Chris Friesen <chris.friesen@...driver.com>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	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

>>>>> "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.

I'm willing to entertain the following, however...

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 95bfb7bfbb9d..75cc51a01860 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2593,7 +2593,8 @@ static void sd_read_block_limits(struct scsi_disk *sdkp)
 	blk_queue_io_min(sdkp->disk->queue,
 			 get_unaligned_be16(&buffer[6]) * sector_sz);
 	blk_queue_io_opt(sdkp->disk->queue,
-			 get_unaligned_be32(&buffer[12]) * sector_sz);
+			 min_t(u32, get_unaligned_be32(&buffer[12]),
+			       sdkp->capacity) * sector_sz);

 	if (buffer[3] == 0x3c) {
 		unsigned int lba_count, desc_count;

-- 
Martin K. Petersen	Oracle Linux Engineering
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