linux-kernel - Re: [GIT PULL] cputime patch for 2.6.30-rc6

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Message-ID: <20090525125034.159ecb78@skybase>
Date:	Mon, 25 May 2009 12:50:34 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Michael Abbott <michael@...neidae.co.uk>,
	Jan Engelhardt <jengelh@...ozas.de>
Subject: Re: [GIT PULL] cputime patch for 2.6.30-rc6

On Tue, 19 May 2009 11:00:35 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> So, I'm really not objecting too much to the patch at hand, but I'd love
> to find a solution to this problem.

It is not hard so solve the problem for /proc/uptime, e.g. like this:

static u64 uptime_jiffies = INITIAL_JIFFIES;
static struct timespec ts_uptime;
static struct timespec ts_idle;

static int uptime_proc_show(struct seq_file *m, void *v)
{
        cputime_t idletime;
        u64 now;
        int i;

        now = get_jiffies_64();
        if (uptime_jiffies != now) {
                uptime_jiffies = now;
                idletime = cputime_zero;
                for_each_possible_cpu(i)
                        idletime = cputime64_add(idletime,
                                                 kstat_cpu(i).cpustat.idle);
                do_posix_clock_monotonic_gettime(&ts_uptime);
                monotonic_to_bootbased(&ts_uptime);
                cputime_to_timespec(idletime, &ts_idle);
        }

        seq_printf(m, "%lu.%02lu %lu.%02lu\n",
                        (unsigned long) ts_uptime.tv_sec,
                        (ts_uptime.tv_nsec / (NSEC_PER_SEC / 100)),
                        (unsigned long) ts_idle.tv_sec,
                        (ts_idle.tv_nsec / (NSEC_PER_SEC / 100)));
        return 0;
}

For /proc/stat it is less clear. Just storing the values in static
variables is not such a good idea as there are lots of values.
10*NR_CPUS + NR_IRQS values to be exact. With NR_CPUS in the thousands
this will waste quite a bit of memory.

I fixed another problem with Michael original patch and added the new
one to reduce the frequency of accesses to kstat_cpu for /proc/uptime.
You'll find both at:

	git://git390.marist.edu/pub/scm/linux-2.6.git cputime

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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