Messages in this thread | | | Date | Wed, 6 May 2009 12:23:48 +0200 | Subject | Re: [PATCH 03/11] tracing: export stats of ring buffers to userspace | From | Frédéric Weisbecker <> |
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2009/5/6 Ingo Molnar <mingo@elte.hu>: > > * Steven Rostedt <rostedt@goodmis.org> wrote: > >> From: Steven Rostedt <srostedt@redhat.com> >> >> This patch adds stats to the ftrace ring buffers: >> >> # cat /debugfs/tracing/per_cpu/cpu0/stats >> entries: 42360 >> overrun: 30509326 >> commit overrun: 0 >> nmi dropped: 0 >> >> Where entries are the total number of data entries in the buffer. >> >> overrun is the number of entries not consumed and were overwritten by >> the writer. >> >> commit overrun is the number of entries dropped due to nested writers >> wrapping the buffer before the initial writer finished the commit. >> >> nmi dropped is the number of entries dropped due to the ring buffer >> lock being held when an nmi was going to write to the ring buffer. >> Note, this field will be meaningless and will go away when the ring >> buffer becomes lockless. >> >> [ Impact: let userspace know what is happening in the ring buffers ] > > nice! I was always wondering about these properties - Frederic > reported that we drop a lot of trace entries when filtering is > enabled, due to the rather stupid: > > reserve-buffer > put-stuff-into-buffer > drop-buffer-if-filter-false > > common sequence we do on heavily filtered input. > > Ingo
But I think I was wrong actually. I looked at it closer recently and the lock events are traced in a raw_local_irq_save section.
So the cause is elsewhere. I haven't had anymore problem with it recently, may be because I'm using a script which disables the events once I finish the tracing. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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