Messages in this thread | | | Date | Mon, 6 Dec 2010 14:04:20 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 3/3] perf record/report: Process events in order |
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On Mon, 6 Dec 2010, Ian Munsie wrote:
> Excerpts from Thomas Gleixner's message of Mon Dec 06 20:20:06 +1100 2010: > > See https://lkml.org/lkml/2010/12/5/45 > > > > Slightly different, but the same idea :) > > Yeah I noted that in my cover email. I meant to get my patches out > before the weekend, but hadn't quite finished cleaning them up to ensure > they didn't break perf when running on a kernel without sample_id_all. > > > > + case PERF_RECORD_HEADER_ATTR: > > > + return ops->attr(event, s); > > > + case PERF_RECORD_HEADER_EVENT_TYPE: > > > + return ops->event_type(event, s); > > > + case PERF_RECORD_HEADER_TRACING_DATA: > > > + return ops->tracing_data(event, s); > > > + case PERF_RECORD_HEADER_BUILD_ID: > > > + return ops->build_id(event, s); > > > > These can be processed unordered. > > I just moved them into this routine to keep all the dispatching in one > place, whether delayed or not. These particular events will still be > processed immediately when encountered in the file. Only >= > PERF_RECORD_MMAP && <= PERF_RECORD_SAMPLE will be delayed via the > perf_session__process_timed function.
Gah. This is nasty. I really prefer the explicit split of instant processed and possibly delayed events. That makes the code clear and easy to extend. I just want to add a new event type at the right place and not worry about magic comparisions in some other place.
> > > { > > > + if (ops->ordered_samples && sample->time == -1ULL) { > > > + dump_printf("Event missing timestamp, switching to unordered processing\n"); > > > + flush_sample_queue(s, ops); > > > + ops->ordered_samples = false; > > > > Why ? The events injected by perf record itself have no timestamps and > > do not need them. So why disabling ordered_samples ? > > For instance, suppose we ran this on an old kernel without support for > timestamps on every event (so timestamps are only on sample events): > > perf record -T > perf report > > If perf report tried to process the events in order, all the events > without timestamps would be processed first -- including the > PERF_RECORD_EXIT event, which would cause every sample not to be > attributed. Falling back means we should get no worse than the old > behaviour, while an upgraded kernel will provide the timestamps and > should not fall back.
Ok, but you'll break existing code which does only care about sample ordering if you do that at the session level unconditionally.
Thanks,
tglx
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