Date: Tue, 1 Nov 2016 14:36:16 -0700 From: Jason Harmening <jason.harmening@gmail.com> To: freebsd-stable@freebsd.org Subject: Re: huge nanosleep variance on 11-stable Message-ID: <1c3f4599-8aef-471a-3a39-49d913f1a4e5@gmail.com> In-Reply-To: <6167392c-c37a-6e39-aa22-ca45435d6088@gmail.com> References: <c88341e2-4c52-ed3c-a469-6446da4415f4@gmail.com> <6167392c-c37a-6e39-aa22-ca45435d6088@gmail.com>
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This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --FeuPRo8Cg75vjqIn3oKdVcFOPkLFb2xpo Content-Type: multipart/mixed; boundary="mwOsF42V3L8V2Klv3dae7EWcGXsbMLrLM"; protected-headers="v1" From: Jason Harmening <jason.harmening@gmail.com> To: freebsd-stable@freebsd.org Message-ID: <1c3f4599-8aef-471a-3a39-49d913f1a4e5@gmail.com> Subject: Re: huge nanosleep variance on 11-stable References: <c88341e2-4c52-ed3c-a469-6446da4415f4@gmail.com> <6167392c-c37a-6e39-aa22-ca45435d6088@gmail.com> In-Reply-To: <6167392c-c37a-6e39-aa22-ca45435d6088@gmail.com> --mwOsF42V3L8V2Klv3dae7EWcGXsbMLrLM Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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. >=20 > 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 t= he >> 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= =2E >> 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 n= ot >> 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 an= y >> guidance on where I should focus my debugging efforts would be much >> appreciated. >> >> Thanks, >> Jason >> >=20 --mwOsF42V3L8V2Klv3dae7EWcGXsbMLrLM-- --FeuPRo8Cg75vjqIn3oKdVcFOPkLFb2xpo Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQF8BAEBCgBmBQJYGQrQXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9w ZW5wZ3AuZmlmdGhob3JzZW1hbi5uZXRENkY3MTQyREU0MTU4MTgyRkZDNUU2ODVC QjlGOEJGOTkyODQxRDFCAAoJELufi/mShB0bIVIIAJWGV1HTR4Q3MjmSKYRmpOd9 VwdriZdNHlP+R6SvjPdxhG2JsAvQsOUvg7UZEu7Or08/JM/SMQOuFL+pXGwHcqE2 e0tl5IDMQHr6JrLweyBiI+td8FuPxqHMDFWm1rsUg6YUkWCEfNYu30vp0Lpuvy6v wn80K0vdBqiLRW60gZsA9KVwt/4TK7VCdgDY/6IajrGLzsxhPcvdGTZA+6QkGf5r WIJfHzXwSm+h4a2hHzpRRSRh2RjalDmgF1yUtuxTmV/NOsuI8SpcT+11zos2jlN6 XmtLcDtgboY8h9rAVQMBibyzsCatQ5fmv443B/TEcgG5DSGfKGjMVXyW4Fqrcew= =z3t/ -----END PGP SIGNATURE----- --FeuPRo8Cg75vjqIn3oKdVcFOPkLFb2xpo--
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