Re: Flush drive cache before issuing ATA_16 from userspace?

[Mark Lord <liml@rtr.ca>]

Tejun Heo wrote:
> Mark Lord wrote:
>>> That's an IDENTIFY (0xEC) command timing out.
>>> The hddtemp program does it's work by issuing IDENTIFY and SMART
>>> commands to the target drive, /dev/sdb in this case.
>>>
>>>     ioctl(3, 0x30d, 0xbfd2c418)
>>>     ioctl(3, 0x31f, 0xbfd2c60c)
>>>     ioctl(3, 0x31f, 0xbfd2c614)
>>>     ioctl(3, 0x31f, 0xbfd2c408)
>>>
>>> So that 0xEC most likely came from the hddtemp program,
>>> since libata doesn't normally issue them after probing.
>>>
>>> So why is it timing out?  Well, these drives have 32MB onboard caches,
>>> and I'm guessing that something (firmware, whatever) tries to empty that
>>> cache before processing the issued IDENTIFY command.  And we time out
>>> before the drive has a chance to actually process the IDENTIFY.
>> ..
>>
>> Another possibility could be some kind of bug in libata or ahci.c.
>> It seems unlikely -- .qc_defer ought to prevent issues -- but I haven't
>> really poked around in there.  And this is a "production" machine :)
>> so we don't like to use it (much) for debugging kernels if we can help it.
> 
> Can you please hack up a program to issue IDENTIFY with different
> timeouts and see when the condition triggers?
..

Yeah, there's a bunch of stuff like that for me to do, someday.  :)

Meanwhile, summer finally arrived here today, so..

Cheers