linux-kernel - Re: [PATCH] Add num_to_str() for speedup /proc/stat

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Date:	Thu, 2 Feb 2012 08:46:30 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrea Righi <andrea@...terlinux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Paul Tuner <pjt@...gle.com>
Subject: Re: [PATCH] Add num_to_str() for speedup /proc/stat

On Wed, 1 Feb 2012 15:43:33 +0100
Andrea Righi <andrea@...terlinux.com> wrote:

> On Mon, Jan 30, 2012 at 02:16:19PM +0900, KAMEZAWA Hiroyuki wrote:
> ...
> > diff --git a/fs/proc/stat.c b/fs/proc/stat.c
> > index 121f77c..0ff3b92 100644
> > --- a/fs/proc/stat.c
> > +++ b/fs/proc/stat.c
> > @@ -89,18 +89,19 @@ static int show_stat(struct seq_file *p, void *v)
> >  	}
> >  	sum += arch_irq_stat();
> >  
> > -	seq_printf(p, "cpu  %llu %llu %llu %llu %llu %llu %llu %llu %llu "
> > -		"%llu\n",
> > -		(unsigned long long)cputime64_to_clock_t(user),
> > -		(unsigned long long)cputime64_to_clock_t(nice),
> > -		(unsigned long long)cputime64_to_clock_t(system),
> > -		(unsigned long long)cputime64_to_clock_t(idle),
> > -		(unsigned long long)cputime64_to_clock_t(iowait),
> > -		(unsigned long long)cputime64_to_clock_t(irq),
> > -		(unsigned long long)cputime64_to_clock_t(softirq),
> > -		(unsigned long long)cputime64_to_clock_t(steal),
> > -		(unsigned long long)cputime64_to_clock_t(guest),
> > -		(unsigned long long)cputime64_to_clock_t(guest_nice));
> > +	seq_puts(p, "cpu ");
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(nice));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(system));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(idle));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(iowait));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(irq));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(softirq));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(steal));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
> > +	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
> > +	seq_putc(p, '\n');
> > +
> >  	for_each_online_cpu(i) {
> >  		/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
> >  		user = kcpustat_cpu(i).cpustat[CPUTIME_USER];
> > @@ -113,26 +114,24 @@ static int show_stat(struct seq_file *p, void *v)
> >  		steal = kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
> >  		guest = kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
> >  		guest_nice = kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
> > -		seq_printf(p,
> > -			"cpu%d %llu %llu %llu %llu %llu %llu %llu %llu %llu "
> > -			"%llu\n",
> > -			i,
> > -			(unsigned long long)cputime64_to_clock_t(user),
> > -			(unsigned long long)cputime64_to_clock_t(nice),
> > -			(unsigned long long)cputime64_to_clock_t(system),
> > -			(unsigned long long)cputime64_to_clock_t(idle),
> > -			(unsigned long long)cputime64_to_clock_t(iowait),
> > -			(unsigned long long)cputime64_to_clock_t(irq),
> > -			(unsigned long long)cputime64_to_clock_t(softirq),
> > -			(unsigned long long)cputime64_to_clock_t(steal),
> > -			(unsigned long long)cputime64_to_clock_t(guest),
> > -			(unsigned long long)cputime64_to_clock_t(guest_nice));
> > +		seq_printf(p, "cpu %d", i);
>                                ^^^^^^
> mmh... if I'm not wrong this looks like an ABI change.
> 
> Thanks,
> -Andrea
> 
> ---
> From: Andrea Righi <andrea@...terlinux.com>
> Subject: procfs: avoid breaking the ABI in /proc/stat
> 
> The speed up of /proc/stat changed the output of the cpu statistics
> adding an extra space between the string "cpu" and the cpu id.
> 
> Restore the old ABI by removing this space.
> 
> Signed-off-by: Andrea Righi <andrea@...terlinux.com>
> ---
>  fs/proc/stat.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/proc/stat.c b/fs/proc/stat.c
> index 0ff3b92..7ed7efa 100644
> --- a/fs/proc/stat.c
> +++ b/fs/proc/stat.c
> @@ -114,7 +114,7 @@ static int show_stat(struct seq_file *p, void *v)
>  		steal = kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
>  		guest = kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
>  		guest_nice = kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
> -		seq_printf(p, "cpu %d", i);
> +		seq_printf(p, "cpu%d", i);


Ah, I'm very soory. And thank you very much catching this early !

-Kame

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