From: Frederic Weisbecker <fweisbec@gmail.com>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Tony Luck <tony.luck@intel.com>,
Wanpeng Li <wanpeng.li@hotmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Thomas Gleixner <tglx@linutronix.de>,
Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@kernel.org>,
Fenghua Yu <fenghua.yu@intel.com>, Rik van Riel <riel@redhat.com>,
Stanislaw Gruszka <sgruszka@redhat.com>
Subject: Re: [PATCH 37/37] s390: Prevent from cputime leaks
Date: Wed, 25 Jan 2017 16:25:20 +0100 [thread overview]
Message-ID: <20170125152518.GA3302@lerouge> (raw)
In-Reply-To: <20170123104456.74cb2ef3@mschwideX1>
On Mon, Jan 23, 2017 at 10:44:56AM +0100, Martin Schwidefsky wrote:
> On Sun, 22 Jan 2017 19:20:13 +0100
> Frederic Weisbecker <fweisbec@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 <schwidefsky@de.ibm.com>
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Paul Mackerras <paulus@samba.org>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> > Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> > Cc: Tony Luck <tony.luck@intel.com>
> > Cc: Fenghua Yu <fenghua.yu@intel.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Rik van Riel <riel@redhat.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Stanislaw Gruszka <sgruszka@redhat.com>
> > Cc: Wanpeng Li <wanpeng.li@hotmail.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@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.
next prev parent reply other threads:[~2017-01-25 15:25 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-22 18:19 [PATCH 00/37] cputime: Convert core use of cputime_t to nsecs v3 Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 01/37] jiffies: Reuse TICK_NSEC instead of NSEC_PER_JIFFY Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 02/37] time: Introduce jiffies64_to_nsecs() Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 03/37] sched: Remove unused INIT_CPUTIME macro Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 04/37] cputime: Convert kcpustat to nsecs Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 05/37] macintosh/rack-meter: Remove cputime_t internal use Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 06/37] cputime: Convert guest time accounting to nsecs Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 07/37] cputime: Special API to return old-typed cputime Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 08/37] cputime: Convert task/group cputime to nsecs Frederic Weisbecker
2017-01-28 11:57 ` Stanislaw Gruszka
2017-01-28 15:28 ` Frederic Weisbecker
2017-01-30 13:54 ` Stanislaw Gruszka
2017-01-30 15:38 ` Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 09/37] alpha: Convert obsolete cputime_t " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 10/37] x86: Convert obsolete cputime type " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 11/37] isdn: " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 12/37] binfmt: " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 13/37] acct: " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 14/37] delaycct: " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 15/37] tsacct: " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 16/37] signal: " Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 17/37] cputime: Increment kcpustat directly on irqtime account Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 18/37] posix-timers: Use TICK_NSEC instead of a dynamically ad-hoc calculated version Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 19/37] posix-timers: Convert internals to use nsecs Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 20/37] itimer: Convert internal cputime_t units to nsec Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 21/37] sched: Remove temporary cputime_t accessors Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 22/37] cputime: Push time to account_user_time() in nsecs Frederic Weisbecker
2017-01-22 18:19 ` [PATCH 23/37] cputime: Push time to account_steal_time() " Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 24/37] cputime: Push time to account_idle_time() " Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 25/37] cputime: Push time to account_system_time() " Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 26/37] cputime: Complete nsec conversion of tick based accounting Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 27/37] vtime: Return nsecs instead of cputime_t to account Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 28/37] cputime: Remove jiffies based cputime Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 29/37] ia64: Move nsecs based cputime headers to the last arch using it Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 30/37] ia64: Convert vtime to use nsec units directly Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 31/37] ia64: Remove unused cputime definitions Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 32/37] s390: Make arch_cpu_idle_time() to return nsecs Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 33/37] powerpc: Remove unused cputime definitions Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 34/37] s390: " Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 35/37] cputime: Remove unused nsec_to_cputime Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 36/37] cputime: Remove asm generic headers Frederic Weisbecker
2017-01-22 18:20 ` [PATCH 37/37] s390: Prevent from cputime leaks Frederic Weisbecker
2017-01-23 9:44 ` Martin Schwidefsky
2017-01-25 15:25 ` Frederic Weisbecker [this message]
2017-01-25 15:40 ` Martin Schwidefsky
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