Messages in this thread | | | From | Anna-Maria Behnsen <> | Subject | Re: [PATCH v10 18/20] timers: Implement the hierarchical pull model | Date | Tue, 06 Feb 2024 11:06:19 +0100 |
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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 :)
Thanks,
Anna-Maria
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