On Mon, 2007-05-14 at 09:40 +0200, Jens Axboe wrote:
> On Fri, May 11 2007, Vasily Tarasov wrote:
> > Hello all,
> > 
> > The function blk_start_queueing() calls __generic_unplug_device()
> > function directly without tracing BLK_TA_UNPLUG_IO action. So I have an
> > odd output of blktrace, when requests go through the plugged queue. I
> > suppose it's a BUG, or do I miss something?
> 
> The unplug trace is meant to log upper layers doing an unplug to start
> IO, not internal use that wants to kick the queue for whatever reasons.
> We could log those as well, but it would be preferential to seperate
> them.
> 
> blk_start_queuing() is one such call, for instance.
> 

Thank you, now I understand it. I believe it is very necessary to trace
internal unplugging (as a separate case), because such trace:

  3,64   1       46     5.227907883 10539  P   R [randreader]
  3,64   1       47     5.227908103 10539  I   R 2068072 + 8
[randreader]
  3,64   1       48     5.227909288 10539  D   R 2068072 + 8
[randreader]
  3,64   1       49     5.227931205 10539  Q   R 2068088 + 112
[randreader]
  3,64   1       50     5.227932222 10539  G   R 2068088 + 112
[randreader]
  3,64   1       51     5.227932827 10539  I   R 2068088 + 112
[randreader]
  3,64   1       52     5.227985593 10539  C   R 2068072 + 8 [0]

looks a bit confusing.

Thank you,
Vasily

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