Sorry, that should be ~*30ms* to get 30fps, though the variance is still up to 500ms for me either way.
On 11/01/16 14:29, Jason Harmening wrote: > repro code is at http://pastebin.com/B68N4AFY if anyone's interested. > > On 11/01/16 13:58, Jason Harmening wrote: >> Hi everyone, >> >> I recently upgraded my main amd64 server from 10.3-stable (r302011) to >> 11.0-stable (r308099). It went smoothly except for one big issue: >> certain applications (but not the system as a whole) respond very >> sluggishly, and video playback of any kind is extremely choppy. >> >> The system is under very light load, and I see no evidence of abnormal >> interrupt latency or interrupt load. More interestingly, if I place the >> system under full load (~0.0% idle) the problem *disappears* and >> playback/responsiveness are smooth and quick. >> >> Running ktrace on some of the affected apps points me at the problem: >> huge variance in the amount of time spent in the nanosleep system call. >> A sleep of, say, 5ms might take anywhere from 5ms to ~500ms from entry >> to return of the syscall. OTOH, anything CPU-bound or that waits on >> condvars or I/O interrupts seems to work fine, so this doesn't seem to >> be an issue with overall system latency. >> >> I can repro this with a simple program that just does a 3ms usleep in a >> tight loop (i.e. roughly the amount of time a video player would sleep >> between frames @ 30fps). At light load ktrace will show the huge >> nanosleep variance; under heavy load every nanosleep will complete in >> almost exactly 3ms. >> >> FWIW, I don't see this on -current, although right now all my -current >> images are VMs on different HW so that might not mean anything. I'm not >> aware of any recent timer- or scheduler- specific changes, so I'm >> wondering if perhaps the recent IPI or taskqueue changes might be >> somehow to blame. >> >> I'm not especially familiar w/ the relevant parts of the kernel, so any >> guidance on where I should focus my debugging efforts would be much >> appreciated. >> >> Thanks, >> Jason >> >
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