On Sun, 21 Mar 2021, Jonathan Schwender wrote: > > On 2/22/21 5:20 PM, Ahmed S. Darwish wrote: > > On Mon, Feb 22, 2021 at 04:28:30PM +0100, Jonathan Schwender wrote: > >> Hi John, > >> > >> This patch adds the option --mainaffinity to specify the affinity of > >> the main pid. > >> This is mainly useful if you want to bind the main thread to a > >> different (e.g. housekeeping ) CPU than the measurement threads. > >> > > Do you also have any numbers showing different results with/without > > "--mainaffinity"? > > Sorry for the delay. I do have some numbers now, and there is a benefit to > using this option if CPU isolation + CAT are used. Otherwise it's not really > visible. > > Rendered Markdown: > https://gist.github.com/jschwe/d4c46026aec57b10a2b0e6f72258b96e > > # Testing proposed cyclictest --mainaffinity option > > System information: > - 2 socket Intel Xeon E5-2643 v4 @ 3.40Ghz > - Turbo boost is disabled. > - Fedora 33 with kernel 5.10.1-rt20 with small patch (see cmdline isolcpus) > - Cmdline: `nosmt isolcpus=domain,managed_irq,wq,rcu,misc,kthread,3,5,7,9,11 > rcu_nocbs=3,5,7,9,11 irqaffinity=0,2,4 maxcpus=12 rcu_nocb_poll nowatchdog > tsc=nowatchdog processor.max_cstate=1 intel_idle.max_cstate=0 > systemd.unified_cgroup_hierarchy=0` > - The additional isolcpus arguments set the HK_FLAG with the corresponding > name. > This cmdline adds all HK_FLAGs usually set by nohz_full, except the > actual > nohz flags `tick` and `timer`. This improves cyclictest latencies on my > system. > - Rteval is running on all CPUs from node 0 + CPU 1, but not on the isolated > CPUs. > - L3 Cache is reserved for the isolated CPUs via `resctrl` (CPU based > allocation) > - Test duration 24 hours, interval 200 µs > > > ## Test 1: 5 cyclictest instance with main pid on same cpu as the measurement > thread > > This test simply starts 5 cyclictest instances (via numactl) with one > measurement thread each and bound to a single > CPU via `--affinity`, so that the main thread is also bound to the same CPU. > >  > > ## Test 2: Single cyclictest instance with --mainaffinity=1 for isolated CPUs > 3,5,7,9,11 > The main thread was placed on CPU 1 via `--mainaffinity` and > `--refresh_on_max` was added for good measure to keep the > logfile small. > >  > > > > > Thanks, > > > > -- > > Ahmed S. Darwish > Jonathan > > Alright, I can imagine how this could be useful. Would you respin the patches against the latest upstream and resend to me? Thanks John
