linux-kernel - Re: [PATCH] PM / suspend: measure the time of filesystem syncing

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Date:   Tue, 05 Feb 2019 12:55:01 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Harry Pan <harry.pan@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, gs0622@...il.com,
        pavel@....cz, len.brown@...el.com, linux-pm@...r.kernel.org
Subject: Re: [PATCH] PM / suspend: measure the time of filesystem syncing

On Sunday, February 3, 2019 6:20:07 AM CET Harry Pan wrote:
> This patch gives the reader an intuitive metric of the time cost by
> the kernel issuing a filesystem sync during suspend; although developer
> can guess by the timestamp of next log or enable the ftrace power event
> for manual calculation, this manner is easier to read and benefits the
> automatic script.
> 
> Signed-off-by: Harry Pan <harry.pan@...el.com>
> ---
>  kernel/power/suspend.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 0bd595a0b610..f3b7c64f2242 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -550,6 +550,8 @@ static void suspend_finish(void)
>  static int enter_state(suspend_state_t state)
>  {
>  	int error;
> +	ktime_t start, end, elapsed;

Why do you need three vars here?  One should be sufficient.

> +	unsigned int elapsed_msecs;
>  
>  	trace_suspend_resume(TPS("suspend_enter"), state, true);
>  	if (state == PM_SUSPEND_TO_IDLE) {
> @@ -570,9 +572,14 @@ static int enter_state(suspend_state_t state)
>  
>  #ifndef CONFIG_SUSPEND_SKIP_SYNC
>  	trace_suspend_resume(TPS("sync_filesystems"), 0, true);
> +	start = ktime_get_boottime();

Why _boottime()?

>  	pr_info("Syncing filesystems ... ");
>  	ksys_sync();
> -	pr_cont("done.\n");
> +	end = ktime_get_boottime();
> +	elapsed = ktime_sub(end, start);
> +	elapsed_msecs = ktime_to_ms(elapsed);
> +	pr_cont("(elapsed %d.%03d seconds) done.\n", elapsed_msecs / 1000,
> +		elapsed_msecs % 1000);
>  	trace_suspend_resume(TPS("sync_filesystems"), 0, false);
>  #endif
>  
>