lkml.org 
[lkml]   [2018]   [Oct]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: livelock with hrtimer cpu_base->lock
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

--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum,
Linux Foundation Collaborative Project

\
 
 \ /
  Last update: 2018-10-12 14:57    [W:0.039 / U:0.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site