Messages in this thread | | | Date | Tue, 17 Sep 2013 08:29:07 -0600 | From | Jens Axboe <> | Subject | Re: BLK_TN_PROCESS events not delivered for all devices |
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On 09/16/2013 03:23 AM, Jan Kara wrote: > Hi, > > I've been looking into a problem where BLK_TN_PROCESS events are not > delivered to all devices which are being traced. This results in process > name being (null) when trace for a single device is parsed. > > The reason for this problem is that trace_note_tsk() is called only if > tsk->btrace_seq != blktrace_seq and it updates tsk->btrace_seq to > blktrace_seq. Thus after a trace for another device is started > BLK_TN_PROCESS event is sent only on behalf of the first device with which > the task interacts. That isn't necessarily the new device thus traces for > some devices accumulate several BLK_TN_PROCESS events for one task while > other have none. Is this a known problem and is this intended to work > better? > > I was thinking how to fix that for a while and it doesn't seem to be > possible without tracking with each block trace which tasks it has been > notified about. And that is relatively expensive...
It is unfortunately a known issue... I have not come up with a good way to fix it either, while keeping it cheap. So if you think of something, do let me know.
-- Jens Axboe
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