Re: [PATCH 1/2] perf: Add sampling of the raw monotonic clock
From: Peter Zijlstra <hidden>
Date: 2014-09-29 15:28:36
Also in:
lkml
On Thu, Sep 18, 2014 at 03:34:32PM +0100, Pawel Moll wrote:
quoted hunk ↗ jump to hunk
@@ -4456,6 +4459,13 @@ static void __perf_event_header__init_id(struct perf_event_header *header, data->cpu_entry.cpu = raw_smp_processor_id(); data->cpu_entry.reserved = 0; } + + if (sample_type & PERF_SAMPLE_CLOCK_RAW_MONOTONIC) { + struct timespec now; + + getrawmonotonic(&now); + data->clock_raw_monotonic = timespec_to_ns(&now); + } }
This cannot work, getrawmonotonic() isn't NMI-safe and there's nothing stopping this being used from NMI context. Also getrawmonotonic() + timespec_to_ns() will make tglx sad, he's just done a tree-wide eradication of silly conversions and now you're adding a ns -> timespec -> ns dance right back. I _think_ you want ktime_get_mono_fast_ns(), but this does bring us right back to the question/discussion on which timebase you'd want to sync again. MONO does make sense for most cases, but I think we've had fairly sane stories for people wanting to sync against other clocks. A well..