Messages in this thread | | | Date | Tue, 6 Feb 2024 11:29:19 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v10 18/20] timers: Implement the hierarchical pull model |
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On Tue, Feb 06, 2024 at 11:06:19AM +0100, Anna-Maria Behnsen wrote: > Frederic Weisbecker <frederic@kernel.org> writes: > > > Le Mon, Feb 05, 2024 at 02:29:34PM +0100, Anna-Maria Behnsen a écrit : > >> Anna-Maria Behnsen <anna-maria@linutronix.de> writes: > >> > >> > Frederic Weisbecker <frederic@kernel.org> writes: > >> > > >> >> Le Thu, Feb 01, 2024 at 05:15:37PM +0100, Anna-Maria Behnsen a écrit : > >> >>> Frederic Weisbecker <frederic@kernel.org> writes: > >> >>> > >> >>> > Le Mon, Jan 15, 2024 at 03:37:41PM +0100, Anna-Maria Behnsen a écrit : > >> >>> > Heh, I was about to say that it's impossible that timer_base_is_idle() > >> >>> > at this stage but actually if we run in nohz_full... > >> >>> > > >> >>> > It happens so that nohz_full is deactivated until rcutree_online_cpu() > >> >>> > which calls tick_dep_clear() but it's a pure coincidence that might > >> >>> > disappear one day. So yes, let's keep it that way. > >> >>> > >> >>> I instrumented the code (with NOHZ FULL and NOHZ_IDLE) to make sure the > >> >>> timer migration hierarchy state 'idle' is in sync with the timer base > >> >>> 'idle'. And this was one part where it was possible that it runs out of > >> >>> sync as I remember correctly. But if I understood you correctly, this > >> >>> shouldn't happen at the moment? > >> >> > >> >> Well, it's not supposed to :-) > >> > > >> > Hmm, let me double check this and run the tests on the instrumented > >> > version... > >> > >> I added a prinkt() to verify what I think I remember. I was able to see > >> the prints. So it seems, that the coincidence that nohz_full is > >> deactivated until rcutree_online_cpu() already disappeared. > > > > Nice, then I guess it can become a WARN_ON. > > Either I misunderstood something, or wasn't able to explain what I > wanted to say. > > I understood, that nohz full is disabled (by coincidence) until > rcutree_online_cpu() which comes after the timer migration CPU hotplug > AP. This means, that the check whether timer base is idle or not, > shouldn't be required in tmigr_cpu_online() to keep cpu idle or mark it > active in the hierarchy. But we could keep it in case coincidence > disappears. No? > > So I added a printk() when timer base is idle in tmigr_cpu_online(). And > I was able to see the prints. This means, nohz full is _not_ disabled > when executing tmigr_cpu_online(), or am I wrong? > > So when I replace the printk() with a WARN_ON() it will definitely > trigger. So I'm not sure if this is what you want to have :)
Yes, silly me, I thought the tick dependency was set on all hotplug operations but it's only cpu down. So this piece doesn't need to change AFAICT.
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