On Mon, Jan 23, 2017 at 10:44:56AM +0100, Martin Schwidefsky wrote: > On Sun, 22 Jan 2017 19:20:13 +0100 > Frederic Weisbecker <fweis...@gmail.com> wrote: > > > The s390 clock has a higher granularity than nanoseconds. 1 nanosec > > equals 4.096 in s390 cputime_t. Therefore we leak a remainder while > > flushing the cputime through cputime_to_nsecs(). > > > > For more precision, make sure we keep that remainder on cputime > > accumulators for later accounting. > > > > Reported-by: Martin Schwidefsky <schwidef...@de.ibm.com> > > Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > Cc: Paul Mackerras <pau...@samba.org> > > Cc: Michael Ellerman <m...@ellerman.id.au> > > Cc: Heiko Carstens <heiko.carst...@de.ibm.com> > > Cc: Martin Schwidefsky <schwidef...@de.ibm.com> > > Cc: Tony Luck <tony.l...@intel.com> > > Cc: Fenghua Yu <fenghua...@intel.com> > > Cc: Peter Zijlstra <pet...@infradead.org> > > Cc: Rik van Riel <r...@redhat.com> > > Cc: Thomas Gleixner <t...@linutronix.de> > > Cc: Ingo Molnar <mi...@kernel.org> > > Cc: Stanislaw Gruszka <sgrus...@redhat.com> > > Cc: Wanpeng Li <wanpeng...@hotmail.com> > > Signed-off-by: Frederic Weisbecker <fweis...@gmail.com> > > NAK. Good intention but the patch is just broken. with 36 of the 37 > patches applied all looks good but the last one completely breaks the > accounting for s390. This is from an idle system: > > top - 10:39:33 up 0 min, 1 user, load average: 0,00, 0,00, 0,00 > Tasks: 106 total, 1 running, 105 sleeping, 0 stopped, 0 zombie > %Cpu0 : 8,9 us, 21,6 sy, 0,0 ni, 0,0 id, 0,0 wa, 10,8 hi, 4,3 si, 54,4 > st > %Cpu1 : 0,0 us, 23,5 sy, 0,0 ni, 0,0 id, 0,0 wa, 19,0 hi, 13,1 si, 44,3 > st > %Cpu2 : 0,0 us, 30,3 sy, 0,0 ni, 0,0 id, 0,0 wa, 14,7 hi, 14,8 si, 40,2 > st > KiB Mem : 1009304 total, 818808 free, 57284 used, 133212 buff/cache > KiB Swap: 1048556 total, 1048556 free, 0 used. 917356 avail Mem
Oh ok. I must have done something wrong. > > There is another issue that affects precision, there is no s390 specific > version of cputime_to_nsecs. The generic version uses cputime_to_usecs > and mulitplies by 1000 to get nano-seconds. That already looses precision. That's right. And that's the point of this patch. I'm not sure we can have a more precise version of cputime_to_nsecs() if 1 nsec == 4.096 cputime_t > > For now just drop that last patch please. Ok, I'm leaving it apart. Thanks.
