On 24 April 2013 16:52, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > On 9 April 2013 20:22, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: >> [Steven replied to a personal Ping!!, including everybody again] >> >> On 9 April 2013 19:25, Steven Rostedt <rostedt@xxxxxxxxxxx> 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.kumar@xxxxxxxxxx> 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. > > Ping!! Ping!! -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
