Re: [PATCH] libata: reduce ATA command timeout to 7secs

[Tejun Heo <htejun@gmail.com>]

[cc'ing Jens, hello]

Mark Lord wrote:
> Tejun Heo wrote:
>> Both ATA and ATAPI devices used the default timeouts defined by SCSI
>> high level driver.  For both disks and ODDs, it was 30secs, which was
>> way too long for disks.  This patch makes most ATA commands time out
>> after 7secs - the de facto ATA command timeout, while leaving ATAPI
>> timeout at 30secs.
> 
> Good patch, LONG overdue.
> 
> But 7 seconds is too short.  I have drives here now that
> take slightly more than 7 seconds to report media errors.
> 
> With this patch, libata will timeout/reset the drive just before
> it had a chance to tell us why it was taking too long.
> 
> The result would be that we might lose data unnecessarily,
> especially in combination with the current SCSI policy of
> blindly failing the entire request when only one sector was bad.

Timeout doesn't indicate media error, so SCSI will retry the command
several times.  So, those two don't interact.

> I've used 10 second timeouts with 100% success over the past 14 years,
> which allows just enough margin (+2) for drives to finish their internal
> retries and report back.
> 
> NACK to 7, ACK to 10 seconds.

Hmmm... I don't care whether 7 or 10.  The biggest reason I chose 7 was
because somebody told me that that's the de-facto default ATA command
timeout && the other os is using it.  I faintly remembers that it was
yourself or Jens.  Or I might be just imagining things again.  :-)

Jens, what do you think about this?

Thanks.

-- 
tejun