linux-kernel - Re: [PATCH v3] rcuscale: Console output claims too few grace periods

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Date:   Fri, 25 Jun 2021 09:44:43 +0800
From:   "Han, Jiangong" <Jiangong.Han@...driver.com>
To:     paulmck@...nel.org
Cc:     dave@...olabs.net, josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, linux-kernel@...r.kernel.org,
        rcu@...r.kernel.org
Subject: Re: [PATCH v3] rcuscale: Console output claims too few grace periods

Hi,  Paul,

I think your words are much clear than mine, no missings, thanks for 
your help.  :)
Thanks for your quickly response again.

Br,

Jiangong


在 2021/6/25 上午12:40, Paul E. McKenney 写道:
> [Please note: This e-mail is from an EXTERNAL e-mail address]
>
> On Thu, Jun 24, 2021 at 10:34:24PM +0800, Jiangong.Han wrote:
>> The rcuscale console output claims N grace periods, numbered from zero
>> to N, which means that there were really N+1 grace periods.  The root
>> cause of this bug is that rcu_scale_writer() stores the number of the
>> last grace period (numbered from zero) into writer_n_durations[me]
>> instead of the number of grace periods. This commit therefore assigns
>> the actual number of grace periods to writer_n_durations[me], and also
>> makes the corresponding adjustment to the loop outputting per-grace-period
>> measurements.
>>
>> Sample of old console output:
>>        rcu-scale: writer 0 gps: 133
>>        ......
>>        rcu-scale:    0 writer-duration:     0 44003961
>>        rcu-scale:    0 writer-duration:     1 32003582
>>        ......
>>        rcu-scale:    0 writer-duration:   132 28004391
>>        rcu-scale:    0 writer-duration:   133 27996410
>>
>> Sample of new console output:
>>        rcu-scale: writer 0 gps: 134
>>        ......
>>        rcu-scale:    0 writer-duration:     0 44003961
>>        rcu-scale:    0 writer-duration:     1 32003582
>>        ......
>>        rcu-scale:    0 writer-duration:   132 28004391
>>        rcu-scale:    0 writer-duration:   133 27996410
>>
>> Signed-off-by: Jiangong.Han <jiangong.han@...driver.com>
>> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> I already have it queued in -rcu here:
>
> 4c154a910344 ("rcuscale: Console output claims too few grace periods")
>
> Or did you find an error in my wordsmithed version of your commit log?
> If so, please point out the error explicitly.  (It looks identical to me,
> but I could easily be missing something.)
>
>                                                          Thanx, Paul
>
>> ---
>>   kernel/rcu/rcuscale.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
>> index dca51fe9c73f..2cc34a22a506 100644
>> --- a/kernel/rcu/rcuscale.c
>> +++ b/kernel/rcu/rcuscale.c
>> @@ -487,7 +487,7 @@ rcu_scale_writer(void *arg)
>>        if (gp_async) {
>>                cur_ops->gp_barrier();
>>        }
>> -     writer_n_durations[me] = i_max;
>> +     writer_n_durations[me] = i_max + 1;
>>        torture_kthread_stopping("rcu_scale_writer");
>>        return 0;
>>   }
>> @@ -561,7 +561,7 @@ rcu_scale_cleanup(void)
>>                        wdpp = writer_durations[i];
>>                        if (!wdpp)
>>                                continue;
>> -                     for (j = 0; j <= writer_n_durations[i]; j++) {
>> +                     for (j = 0; j < writer_n_durations[i]; j++) {
>>                                wdp = &wdpp[j];
>>                                pr_alert("%s%s %4d writer-duration: %5d %llu\n",
>>                                        scale_type, SCALE_FLAG,
>> --
>> 2.17.1
>>