<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Dec 5, 2017 at 2:16 PM, Lionel Landwerlin <span dir="ltr"><<a href="mailto:lionel.g.landwerlin@intel.com" target="_blank">lionel.g.landwerlin@intel.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hey Sagar,<br>
<br>
Sorry for the delay looking into this series.<br>
I've done some userspace/UI work in GPUTop to try to correlate perf samples/tracepoints with i915 perf reports.<br>
<br>
I wanted to avoid having to add too much logic into the kernel and tried to sample both cpu clocks & gpu timestamps from userspace.<br>
So far that's not working. People more knowledgable than I would have realized that the kernel can sneak in work into syscalls.<br>
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.<br>
Anyway the UI work won't go to waste :)<br>
<br>
I'm thinking to go with your approach.<br>
>From my experiment with gputop, it seems we might want to use a different cpu clock source though or make it configurable.<br>
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.<br></blockquote><div><br></div><div>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.</div><div><br></div><div>E.g. here's some discussion around why vblank events use CLOCK_MONOTINIC: <a href="https://lists.freedesktop.org/archives/dri-devel/2012-October/028878.html">https://lists.freedesktop.org/archives/dri-devel/2012-October/028878.html</a><br></div><div><br></div><div>Br,</div><div>- Robert<br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
I'll look at adding some tests for this too.<br>
<br>
Thanks,<br>
<br>
-<br>
Lionel<span class="gmail-im gmail-HOEnZb"><br>
<br>
On 15/11/17 12:13, Sagar Arun Kamble wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
We can compute system time corresponding to GPU timestamp by taking a<br>
reference point (CPU monotonic time, GPU timestamp) and then adding<br>
delta time computed using timecounter/cyclecounter support in kernel.<br>
We have to configure cyclecounter with the GPU timestamp frequency.<br>
Earlier approach that was based on cross-timestamp is not needed. It<br>
was being used to approximate the frequency based on invalid assumptions<br>
(possibly drift was being seen in the time due to precision issue).<br>
The precision of time from GPU clocks is already in ns and timecounter<br>
takes care of it as verified over variable durations.<br>
<br>
This series adds base timecounter/cyclecounter changes and changes to<br>
get GPU and CPU timestamps in OA samples.<br>
<br>
Sagar Arun Kamble (1):<br>
drm/i915/perf: Add support to correlate GPU timestamp with system time<br>
<br>
Sourab Gupta (3):<br>
drm/i915/perf: Add support for collecting 64 bit timestamps with OA<br>
reports<br>
drm/i915/perf: Extract raw GPU timestamps from OA reports<br>
drm/i915/perf: Send system clock monotonic time in perf samples<br>
<br>
drivers/gpu/drm/i915/i915_drv.<wbr>h | 11 ++++<br>
drivers/gpu/drm/i915/i915_perf<wbr>.c | 124 ++++++++++++++++++++++++++++++<wbr>++++++++-<br>
drivers/gpu/drm/i915/i915_reg.<wbr>h | 6 ++<br>
include/uapi/drm/i915_drm.h | 14 +++++<br>
4 files changed, 154 insertions(+), 1 deletion(-)<br>
<br>
</blockquote>
<br></span><div class="gmail-HOEnZb"><div class="gmail-h5">
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