Peter Zijlstra <pet...@infradead.org> writes:
> On Mon, Jun 03, 2019 at 12:43:09PM +0800, Liangyan wrote:
>> From: "liangyan.ply" <liangyan....@linux.alibaba.com>
>>
>> start_cfs_slack_bandwidth() will restart the quota slack timer,
>> if it is called frequently, this timer will be restarted continuously
>> and may have no chance to expire to unthrottle cfs tasks.
>> This will cause that the throttled tasks can't be unthrottled in time
>> although they have remaining quota.
>
> This looks very similar to the patch from Ben here:
>
> https://lkml.kernel.org/r/xm26blzlyr9d....@bsegall-linux.svl.corp.google.com
Yeah, it should do the same sort of thing, but testing hrtimer_active
is racy (we could miss restarting the timer if it's just dropped the
cfsb lock but hasn't finished yet), so the extra accounting flag is
needed.
>
>>
>> Signed-off-by: Liangyan <liangyan.p...@linux.alibaba.com>
>> ---
>> kernel/sched/fair.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index d90a64620072..fdb03c752f97 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -4411,9 +4411,11 @@ static void start_cfs_slack_bandwidth(struct
>> cfs_bandwidth *cfs_b)
>> if (runtime_refresh_within(cfs_b, min_left))
>> return;
>>
>> - hrtimer_start(&cfs_b->slack_timer,
>> + if (!hrtimer_active(&cfs_b->slack_timer)) {
>> + hrtimer_start(&cfs_b->slack_timer,
>> ns_to_ktime(cfs_bandwidth_slack_period),
>> HRTIMER_MODE_REL);
>> + }
>> }
>>
>> /* we know any runtime found here is valid as update_curr() precedes return
>> */
>> --
>> 2.14.4.44.g2045bb6
>>
