On 9 April 2013 20:22, Viresh Kumar <viresh.ku...@linaro.org> wrote: > [Steven replied to a personal Ping!!, including everybody again] > > On 9 April 2013 19:25, Steven Rostedt <rost...@goodmis.org> wrote: >> On Tue, 2013-04-09 at 14:05 +0530, Viresh Kumar wrote: >>> Ping!! >>> >> >> Remind me again. What problem are you trying to solve? > > I was trying to migrate a running timer which arms itself, so that we don't > keep a cpu busy just for servicing this timer. > >>> On 20 March 2013 20:43, Viresh Kumar <viresh.ku...@linaro.org> wrote: >>> > >>> > Hi Steven/Thomas, >>> > >>> > I came back to this patch after completing some other stuff and posting >>> > wq part of this patchset separately. >>> > >>> > I got your point and understand how this would fail. >>> > >>> > @Thomas: I need your opinion first. Do you like this concept of migrating >>> > running timer or not? Or you see some basic problem with this concept? >> >> I'll let Thomas answer this, but to me, this sounds really racy. > > Sure. > >>> > If no (i.e. i can go ahead with another version), then i have some >>> > solution to >>> > fix earlier problems reported by Steven: >>> > >>> > The problem lies with del_timer_sync() which just checks >>> > base->running_timer != timer to check if timer is currently running or >>> > not. >>> > >>> > What if we add another variable in struct timer_list, that will store if >>> > we are >>> > running timer callback or not. And so, before we call callback in timer >>> > core, >>> > we will set this variable and will reset it after finishing callback. >>> > >>> > del_timer_sync() will have something like: >>> > >>> > if (base->running_timer != timer) >>> > remove timer and return; >> >> For example, this didn't fix the issue. You removed the timer when it >> was still running, because base->running_timer did not equal timer. > > You are correct and i was stupid. I wanted to write this instead: > > del_timer_sync() will have something like: > > if (base->running_timer != timer) > if (timer->running_callback) > go back to its loop... > else > remove timer and return; > > i.e. if we aren't running on our base cpu, just check if our callback is > executing somewhere else due to migration.
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