linux-kernel - Re: [PATCH] rcu-scale: change rcu-scale report.

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Message-ID: <20210609203711.GL4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Wed, 9 Jun 2021 13:37:11 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     "Jiangong.Han" <jiangong.han@...driver.com>
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] rcu-scale: change rcu-scale report.

On Sat, Jun 05, 2021 at 03:00:19PM +0800, Jiangong.Han wrote:
> The report on rcu-scale shows there are N grace periods, and gps
> are listed from 0 to N-1.
> This commit make writer_n_durations stores the counts of gps,
> change the listed gps index begin from 1 to N.
> 
> From
>     [ 8306.087880] rcu-scale: writer 0 gps: 133
>     ......
>     [ 8307.864630] rcu-scale:    0 writer-duration:     0 44003961
>     [ 8307.935711] rcu-scale:    0 writer-duration:     1 32003582
>     ......
>     [ 8316.472860] rcu-scale:    0 writer-duration:   131 28004391
>     [ 8316.538498] rcu-scale:    0 writer-duration:   132 27996410
> 
> to
>     [ 8306.087880] rcu-scale: writer 0 gps: 133
>     ......
>     [ 8307.864630] rcu-scale:    0 writer-duration:     1 44003961
>     [ 8307.935711] rcu-scale:    0 writer-duration:     2 32003582
>     ......
>     [ 8316.472860] rcu-scale:    0 writer-duration:   132 28004391
>     [ 8316.538498] rcu-scale:    0 writer-duration:   133 27996410
> 
> Signed-off-by: Jiangong.Han <jiangong.han@...driver.com>

You lost me on this one.  Why is this helpful?  And how does the change
shown below actually result in the output shown above, given that
rcu_scale_cleanup() still starts j at zero?

							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
>