On Tue, Dec 5, 2017 at 2:16 PM, Lionel Landwerlin < lionel.g.landwer...@intel.com> wrote:
> Hey Sagar, > > Sorry for the delay looking into this series. > I've done some userspace/UI work in GPUTop to try to correlate perf > samples/tracepoints with i915 perf reports. > > I wanted to avoid having to add too much logic into the kernel and tried > to sample both cpu clocks & gpu timestamps from userspace. > So far that's not working. People more knowledgable than I would have > realized that the kernel can sneak in work into syscalls. > So result is that 2 syscalls (one to get the cpu clock, one for the gpu > timestamp) back to back from the same thread leads to time differences of > anywhere from a few microseconds to in some cases close to 1millisecond. So > it's basically unworkable. > Anyway the UI work won't go to waste :) > > I'm thinking to go with your approach. > From my experiment with gputop, it seems we might want to use a different > cpu clock source though or make it configurable. > The perf infrastructure allows you to choose what clock you want to use. > Since we want to avoid time adjustments on that clock (because we're adding > deltas), a clock monotonic raw would make most sense. > I would guess the most generally useful clock domain to correlate with the largest number of interesting events would surely be CLOCK_MONOTONIC, not _MONOTONIC_RAW. E.g. here's some discussion around why vblank events use CLOCK_MONOTINIC: https://lists.freedesktop.org/archives/dri-devel/2012-October/028878.html Br, - Robert > I'll look at adding some tests for this too. > > Thanks, > > - > Lionel > > On 15/11/17 12:13, Sagar Arun Kamble wrote: > >> We can compute system time corresponding to GPU timestamp by taking a >> reference point (CPU monotonic time, GPU timestamp) and then adding >> delta time computed using timecounter/cyclecounter support in kernel. >> We have to configure cyclecounter with the GPU timestamp frequency. >> Earlier approach that was based on cross-timestamp is not needed. It >> was being used to approximate the frequency based on invalid assumptions >> (possibly drift was being seen in the time due to precision issue). >> The precision of time from GPU clocks is already in ns and timecounter >> takes care of it as verified over variable durations. >> >> This series adds base timecounter/cyclecounter changes and changes to >> get GPU and CPU timestamps in OA samples. >> >> Sagar Arun Kamble (1): >> drm/i915/perf: Add support to correlate GPU timestamp with system time >> >> Sourab Gupta (3): >> drm/i915/perf: Add support for collecting 64 bit timestamps with OA >> reports >> drm/i915/perf: Extract raw GPU timestamps from OA reports >> drm/i915/perf: Send system clock monotonic time in perf samples >> >> drivers/gpu/drm/i915/i915_drv.h | 11 ++++ >> drivers/gpu/drm/i915/i915_perf.c | 124 ++++++++++++++++++++++++++++++ >> ++++++++- >> drivers/gpu/drm/i915/i915_reg.h | 6 ++ >> include/uapi/drm/i915_drm.h | 14 +++++ >> 4 files changed, 154 insertions(+), 1 deletion(-) >> >> > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx >
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