Messages in this thread | | | Date | Tue, 17 Sep 2013 22:31:31 +0200 | From | Jan Kara <> | Subject | Re: BLK_TN_PROCESS events not delivered for all devices |
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On Tue 17-09-13 12:23:33, Jens Axboe wrote: > On 09/17/2013 11:10 AM, Jan Kara wrote: > > On Tue 17-09-13 08:29:07, Jens Axboe wrote: > >> 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. > > Hum... How about linking all running block traces (struct blk_trace) in a > > linked list and sending BLK_TN_PROCESS to all the traces? Sure we will be > > spamming with BLK_TN_PROCESS a bit but starting a trace isn't such a common > > thing so it shouldn't be too bad. What do you think? > > That might be good enough. I'm not worried about start/stop type > expenses, those things generally don't matter. And the list wont add any > fast path overhead when tracing. OK, I've sent you a patch which does the trick for me.
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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