Re: blkparse unplug question

[Josh Hunt <joshhunt00@xxxxxxxxx>]

Vasily

Thanks for the response. I apologize, but can you easily explain or
point me in the direction of some documentation describing the
difference b/t the plug queue and the io queue? In my observation of
the blktrace log, the # of requests appears to be going up in my case,
before eventually (I guess) those requests get flushed to the device.
When I set slice_idle to 0 for CFQ I never see these #s getting above
1. I'm just trying to better understand how changing this value is
causing the requests to apparently get flushed from the io queue
faster (or seemingly so.)

I thought about using debugfs for the block->inode lookup but wasn't
sure. Thanks!

Josh

On Wed, Mar 7, 2012 at 12:09 PM, Vasily Tarasov <tarasov@xxxxxxxxxxx> wrote:
> The value after the process name ("31" in your trace snip) is the
> number of requests flushed from the plug queue to the I/O queue during
> the unplug.
>
> To identify which inode a block belongs to you can try to use file
> system specific utils: e.g., xfs_bmap for xfs, debugfs for ext2/3.
> Also there are FIBMAP and FIEMAP ioctls that can help you. Another
> ways is to instrument your file system's code to produce a trace/map
> of blocks; well, if you have time for that ;)
>
> HTH,
> Vasily
>
> On Wed, Mar 7, 2012 at 10:06 AM, Josh Hunt <joshhunt00@xxxxxxxxx> wrote:
>> I am trying to debug a stall I am seeing with CFQ and in the
>> blktrace/blkparse output I see unplugging lines like the following:
>>
>> 8,3    1     7809  1532.225997730   168  U   N [sync_supers] 31
>>
>> My question is what does the value after the process name represent? I
>> see this value increasing from 1, I believe, and then eventually the
>> value appears to get reset.
>>
>> I was also wondering if it is possible to translate the block
>> information provided in blktrace to the corresponding inode?
>>
>> Thanks for your help!
>> Josh
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrace" in
>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>



-- 
Josh
--
To unsubscribe from this list: send the line "unsubscribe linux-btrace" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html