Messages in this thread | | | Date | Wed, 7 May 2014 16:06:43 +0530 | Subject | Re: [PATCH V2] clocksource: register cpu notifier to remove timer from dying CPU | From | Viresh Kumar <> |
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On 7 May 2014 15:38, Thomas Gleixner <tglx@linutronix.de> wrote: > On Wed, 9 Apr 2014, Viresh Kumar wrote: >> This patch tries to fix this by registering cpu notifiers from clocksource core, >> only when we start clocksource-watchdog. And if on the CPU_DEAD notification it >> is found that dying CPU was the CPU on which this timer is queued on, then it is >> removed from that CPU and queued to next CPU. > > Gah, no. We realy don't want more notifier crap.
Agreed, and could have used the generic ones, probably.
> It's perfectly fine for the watchdog timer to be moved around on cpu > down.
Functionally? Yes. Then handler doesn't have any CPU specific stuff to do here and so queuing it on any cpu is fine.
> And the timer itself is not pinned at all. add_timer_on() does > not set the pinned bit.
The perception I had is this: - mod_timer() is a more complicated form of add_timer() as it has to tackle with migration and removal of timers as well. Otherwise they should work in similar way. - There is no PINNED bit which can be set, its just a parameter to __mod_timer() to decide which CPU the timer should fire on. - And by the 'name add_timer_on()', we must guarantee that timer fires on the CPU its being added to, otherwise it may break things for many. There might be users which want to run the handler on a particular CPU due to some CPU-specific stuff they want to do. And have used add_timer_on()...
But looking at your reply, it looks that add_timer_on() doesn't guarantee that timer would fire on the CPU mentioned? Is that the case for mod_timer_pinned() as well ?
And if that's the case what do we want should we do with these timers (i.e. ones added with add_timer_on or mod_timer_pinned) when we try to quiesce a cpu using cpuset.quiesce [1]?
-- viresh
[1] https://lkml.org/lkml/2014/4/4/99
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