Re: [PATCH 2/3] perf events: Introduce realtime clock event
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From: Peter Zijlstra <peterz@infradead.org>
Date: 2011-02-18 11:12:51
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On Thu, 2011-02-17 at 22:53 -0700, David Ahern wrote:
The motivation for this event is to convert perf_clock() time stamps to wall-clock (gettimeofday()) equivalents, including adjustments made by NTP (e.g., for comparing perf events to other log files).
This patch is based on the monotonic patch by Arnaldo Carvalho de Melo [off-list ref]. (NOTE: Comments from the last review of the timehist patch series suggested calling this a monotonic clock. I am not trying to be dense here; since gettimeofday maps to realtime clock I think that is the better name for it.)
Well, the idea was to use CLOCK_MONOTONIC, not to call CLOCK_REALTIME monotonic. I'm really not sure why you want CLOCK_REALTIME and I think CLOCK_MONOTONIC is more useful (I'd argue you want your system logs to contain both, every admin who's ever had to untangle what happened during DST switches will agree)
quoted hunk ↗ jump to hunk
@@ -5610,6 +5612,13 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer) perf_sample_data_init(&data, 0); data.period = event->hw.last_period; + if (event->attr.sample_type & PERF_SAMPLE_RAW) + { + raw.size = sizeof(u64); + raw.data = &event->count; + data.raw = &raw; + } + regs = get_irq_regs(); if (regs && !perf_exclude_event(event, regs)) {
Why!? you already keep ->count = ktime_get_real(), so simply reading the count value will get you the timestamp.. this is superfluous at best.