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On 12/22/2017 10:45 AM, Sagar Arun
Kamble wrote:
On 12/7/2017 1:32 AM, Lionel
Landwerlin wrote:
I've
put together some trival IGT tests :
https://github.com/djdeath/intel-gpu-tools/commits/wip/djdeath/cpu-timestamps
With a few changes which I pointed in the review :
https://github.com/djdeath/linux/commit/d0e4cf4d3f464491b4ffe97d112284d1ce73656d
Put together it seems to work relatively well.
There is still a small drift happening between the 2 timestamps.
I've noticed over a 160ms of OA reports, there is a accumulated
difference of ~35us between the GPU timestamp and cpu
timestamps.
I may be doing something wrong with the scaling in the tests, or
maybe there is an issue in the kernel, or both.
Went through the testcase. scaled_gpu_delta calculation is same as
what timecounter does in kernel for calculating system_time
corresponding
to gpu timestamp hence we don't see much of delta between these
two times/time deltas.
Ideally we should be testing the system time delta by sampling
system time and gpu timestamp atomically (which isn't feasible
unless we do some precise adjustments)
I have attempted to check these two times/delta by sampling them
in debugfs and reading over variable periods manually and checking
the delta.
https://github.com/sakamble/i915-timestamp-support/commit/03be3056752d7b05a02cd01f5c20b3fcfcf18395
It is showing that delta is less than 10us in most cases for 30min
and occasionally around 20-30us. Again this delta might be because
of initial time setting as well.
timecounter initializing system time and gpu clocks as pair should
be highly accurate for which I have currently taken 350us start
offset.
I think gpu timestamp clock is highly stable as seen in my testing
on SKL. I think this clock is used for calculations in GuC too so
will
be good to get confirmation about the stability of this clock from
them and HW team.
systemd-udevd-169 [001] .... 3.035812:
i915_driver_load: sys start time: 1512308011156099790
systemd-udevd-169 [001] d... 3.036012:
i915_cyclecounter_read: 52025098974
cat-1654 [001] .... 52.407957:
i915_cyclecounter_read: 52617562292
cat-1654 [001] .... 52.407958:
i915_timestamp_info: sys time: 1512308060527894638
cat-1654 [001] .... 52.407958:
i915_timestamp_info: ts: 52617562292 device time:
1512308060528043050
cat-1684 [001] .... 177.239733:
i915_cyclecounter_read: 54115543581
cat-1684 [001] .... 177.239736:
i915_timestamp_info: sys time: 1512308185359666602
cat-1684 [001] .... 177.239737:
i915_timestamp_info: ts: 54115543581 device time:
1512308185359817372
cat-1693 [001] .... 329.820374:
i915_cyclecounter_read: 55946511277
cat-1693 [001] .... 329.820377:
i915_timestamp_info: sys time: 1512308337940301732
cat-1693 [001] .... 329.820378:
i915_timestamp_info: ts: 55946511277 device time:
1512308337940458996
<delta between system time delta and gpu time delta for above
two samples (177, 329) = 6494ns>
cat-1702 [001] .... 506.980313:
i915_cyclecounter_read: 58072430542
cat-1702 [001] .... 506.980315:
i915_timestamp_info: sys time: 1512308515100233102
cat-1702 [001] .... 506.980317:
i915_timestamp_info: ts: 58072430542 device time:
1512308515100398084
<delta between system time delta and gpu time delta
for above two samples (329, 506) = 6494ns>
Fixing typo here:
<delta between system time delta and gpu time delta for above two
samples (329, 506) = 7718ns>
I'll build the GPUTop parts and see if the results make sense.
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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