I too have been trying to get below 1ms (heck, 3ms) precision or at least, resolution. I came up with the most promising thing I can think of for interactions in a multithreaded environment yet, I think. glibc has long mapped the kernel clock page into process memory, so i was thinking (hoping) that mmaping that on top of itself a zillion times and using that as my test data source for writes out across the network I'd get some really fine grained insights.
Haven't got around to it yet. On Sat, Dec 4, 2021 at 3:01 PM David P. Reed <dpr...@deepplum.com> wrote: > > I agree with your broad assessment, Jonathan. > > > > The self-interference problem within a host isn't just a network problem. > It's a user-space scheduler problem as well. > > > > There are lots of interactions between user-space scheduler (in the case of > Linux, the "Completely Fair Scheduler" and its quantum, which is set by the > HZ variable at boot) and the network stack in the kernel. This interactions > have non-trivial effects when mutliple flows are independently created by > concurrent processes). > > > > Lately, I've been studying, for reasons related to my day job, the complex > interactions of timing at sub-millisecond scale among threads and processes > on a single system in Linux. I/O driven by threads become highly correlated, > and so assuming "independence" among flow timing is just not a good > assumption. > > > > The paper observes the results of "dependencies" that couple/resonate. > > > > On Friday, December 3, 2021 7:09pm, "Jonathan Morton" <chromati...@gmail.com> > said: > > > > On 4 Dec, 2021, at 12:27 am, Dave Taht <dave.t...@gmail.com> wrote: > > > > > > > > https://jonathankua.github.io/preprints/jkua-ieeelcn2021_understanding_ar_preprint-20jul2021.pdf > > > > > > I would love it if somehow the measured effects of chunklets against > > > cake's > > per-host/per flow fq was examined one day. > > > > I haven't actually measured it, but based on what the above paper says, I > > can make > > some firm predictions: > > > > 1: When competing against traffic to the same local host, the performance > > effects > > they describe will be present. > > > > 2: When competing against traffic to a different local-network host, the > > performance effects they describe will be attenuated or even entirely > > absent. > > > > 3: They noted one or two cases of observable effects of hash collisions in > > their > > tests with FQ-Codel. These will be greatly reduced in prevalence with Cake, > > due > > to the set-associative hash function which specifically addresses that > > phenomenon. > > > > - Jonathan Morton > > _______________________________________________ > > Cake mailing list > > Cake@lists.bufferbloat.net > > https://lists.bufferbloat.net/listinfo/cake > > -- I tried to build a better future, a few times: https://wayforward.archive.org/?site=https%3A%2F%2Fwww.icei.org Dave Täht CEO, TekLibre, LLC _______________________________________________ Cake mailing list Cake@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/cake
