Re: Flush drive cache before issuing ATA_16 from userspace?

[Tejun Heo <htejun@gmail.com>]

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?

Thanks.

-- 
tejun