Messages in this thread | | | Date | Fri, 12 Oct 2018 05:55:28 -0700 | From | Sodagudi Prasad <> | Subject | Re: livelock with hrtimer cpu_base->lock |
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On 2018-10-10 09:49, Will Deacon wrote: > Hi Prasad, > > On Tue, Oct 09, 2018 at 01:56:14PM -0700, Sodagudi Prasad wrote: >> This is regarding - thread "try to fix contention between >> expire_timers and >> try_to_del_timer_sync". >> https://lkml.org/lkml/2017/7/28/172 >> >> I think this live lockup issue was discussed earlier but the final set >> of >> changes were not concluded. > > Well we basically need a way to pick a value for > CPU_RELAX_WFE_THRESHOLD. > Do you have any ideas? It could be determined at runtime if necessary. > Hi Will,
Please share what are values need to be tried for CPU_RELAX_WFE_THRESHOLD.
It would be great if it can be determined from runtime. Please let me know if any testing need to be done with dynamic detection patch.
-Thanks, Prasad
>> I would like to check whether you have new updates on this issue or >> not. >> This problem is observed with 4.14 .64 stable kernel too. >> We see this problem 2 times in overnight testing. >> >> I have to add the following code to avoid live lock. I am thinking >> that >> fixing this at the cpu_relax() level. >> >> +++ b/kernel/time/hrtimer.c >> @@ -52,6 +52,7 @@ >> #include <linux/timer.h> >> #include <linux/freezer.h> >> #include <linux/compat.h> >> +#include <linux/delay.h> >> >> #include <linux/uaccess.h> >> >> @@ -152,6 +153,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const >> struct hrtimer *timer, >> raw_spin_unlock_irqrestore(&base->cpu_base->lock, *flags); >> } >> cpu_relax(); >> + udelay(1); >> } >> } >> >> @@ -1067,6 +1069,7 @@ int hrtimer_cancel(struct hrtimer *timer) >> if (ret >= 0) >> return ret; >> cpu_relax(); >> + udelay(1); >> } >> } >> EXPORT_SYMBOL_GPL(hrtimer_cancel); > > This is just another bodge and likely to hurt in places where 1us is > excessive because there isn't contention. > > Will
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