980003 - support sub-millisecond sampling in SPS profiler on b2g

Status: RESOLVED WONTFIX

(Core :: Gecko Profiler, defect)

Description

[Ben Kelly [:bkelly, not reviewing]]

Now that we have b2g running on some high end devices like nexus-4 and nexus-5, we should consider supporting finer grained sampling rates.

While investigating bug 977975 I hacked the profiler to sample at 0.25ms.  The device ran fine and the profile looked reasonable.

The issue I ran into, though, was cleopatra does not seem to let you select stacks to inspect at fractional ms boundaries.  So I could only look at every 4th stack, etc.

Having a nicer way to select the sub-second sampling would be nice too.  Changing the command line argument to be parsed as a floating point value should be enough to support that.

Comment 1

[Benoit Girard (:BenWa)]

I started some work on this in bug 820048 but you're right we should continue this effort. Sub millisecond profiling would be a big win for graphics so that we can peek into a single frame further (in the order of 15ms).

Cleopatra will need to be adapted and a lot of the profiler frontend like profile.sh and the profiler addon to exposed ways to specify a microsecond.

The other part is the sampling doesn't account for the time it takes to collect a sample so the sampling drifts causing holes in the profile. Fixing that will fix some holes (not all). This problem will be much bigger at microsecond profiling ranges.

Comment 2

[Benoit Girard (:BenWa)]

Bug 980030 might help.

Comment 3

[Markus Stange [:mstange]]

As far as I can tell this is working fine at least on Mac. We don't need to worry about B2G any more. I haven't tested other platforms, especially Android.