On Thu, Feb 08, 2024 at 12:54:58AM -0500, Joel Fernandes wrote: ... > >> Slightly related, but one of the things we are wondering also is how > >> much of the overhead for your nohz-full and lazy-RCU test (on top of > >> baseline - that is just CONFIG_HZ=1000 without nohz-full or nocbs) is > >> because of just using NOCB. Uladsizlau mentioned he might run a test > >> for comparing along those lines as well. > > > > Just to clarify, "lazy rcu on" results are just with rcu_nocb=all and > > lazy RCUs enabled (and HZ=1000), so without nohz_full. > > > > If I enable only nohz_full=all (without rcu_nocb) I see something like > > this: > > Ok. I did want to mention nohz_full implies rcu_nocb on the same CPUs as well. > > Its also mentioned in the boot param docs on the last line of the description: > > nohz_full= [KNL,BOOT,SMP,ISOL] > The argument is a cpu list, as described above. > In kernels built with CONFIG_NO_HZ_FULL=y, set > the specified list of CPUs whose tick will be stopped > whenever possible. The boot CPU will be forced outside > the range to maintain the timekeeping. Any CPUs > in this list will have their RCU callbacks offloaded, > just as if they had also been called out in the > rcu_nocbs= boot parameter. Ah I didn't realize that, it definitely makes sense, thanks for clarifying it. Then basically in the results that I posted the difference is "nohz_full=all+rcu_nocb=all" vs "rcu_nocb=all+lazy_RCU=on". > > (btw, I am a bit slow to respond to email due to being ill). Get well soon! > > thanks, > > - Joel -Andrea
