On 12/5/2017 8:07 PM, Lionel Landwerlin wrote:
On 05/12/17 14:28, Robert Bragg wrote:
On Tue, Dec 5, 2017 at 2:16 PM, Lionel Landwerlin
<lionel.g.landwer...@intel.com
<mailto: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
Thanks Rob, then I guess making it configurable when opening the
stream would be the safest option.
All timecounter users today rely on monotonic clock (Can request for clock
real/wall time, clock boot time, clock tai time
corresponding to monotonic clock).
Agree that we will need to have configuration option about clock to be used
like in trace_clock in ftrace.
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(-)
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