On 11/23/2013 05:30 PM, Sylwester Nawrocki wrote: > Hi, > > On 11/23/2013 12:25 PM, Hans Verkuil wrote: >> Hi Wade, >> >> On 11/22/2013 08:48 PM, Wade Farnsworth wrote: >>> Add tracepoints to the QBUF and DQBUF ioctls to enable rudimentary >>> performance measurements using standard kernel tracers. >>> >>> Signed-off-by: Wade Farnsworth<wade_farnsworth@xxxxxxxxxx> >>> --- >>> >>> This is the update to the RFC patch I posted a few weeks back. I've added >>> several bits of metadata to the tracepoint output per Mauro's suggestion. >> >> I don't like this. All v4l2 ioctls can already be traced by doing e.g. >> echo 1 (or echo 2)>/sys/class/video4linux/video0/debug. >> >> So this code basically duplicates that functionality. It would be nice to be able >> to tie in the existing tracing code (v4l2-ioctl.c) into tracepoints. > > I think it would be really nice to have this kind of support for standard > traces at the v4l2 subsystem. Presumably it could even gradually replace > the v4l2 custom debug infrastructure. > > If I understand things correctly, the current tracing/profiling > infrastructure > is much less invasive than inserting printks all over, which may cause > changes > in control flow. I doubt the system could be reliably profiled by > enabling all > those debug prints. > > So my vote would be to add support for standard tracers, like in other > subsystems in the kernel. The reason for the current system is to trace which ioctls are called in what order by a misbehaving application. It's very useful for that, especially when trying to debug user problems. I don't mind switching to tracepoints as long as this functionality is kept one way or another. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
