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

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

On Tue, 19 May 2009 11:00:35 +0200
Peter Zijlstra <peterz@infradead.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.