linux-toradex.git/kernel/sched/cputime.c, branch v4.9.88

sched/irqtime: Consolidate irqtime flushing code

2016-09-30T09:46:41+00:00

The code performing irqtime nsecs stats flushing to kcpustat is roughly
the same for hardirq and softirq. So lets consolidate that common code.

Signed-off-by: Frederic Weisbecker 
Reviewed-by: Rik van Riel 
Cc: Eric Dumazet 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Link: http://lkml.kernel.org/r/1474849761-12678-6-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar

sched/irqtime: Consolidate accounting synchronization with u64_stats API

2016-09-30T09:46:40+00:00

The irqtime accounting currently implement its own ad hoc implementation
of u64_stats API. Lets rather consolidate it with the appropriate
library.

Signed-off-by: Frederic Weisbecker 
Reviewed-by: Rik van Riel 
Cc: Eric Dumazet 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Link: http://lkml.kernel.org/r/1474849761-12678-5-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar

sched/irqtime: Remove needless IRQs disablement on kcpustat update

2016-09-30T09:46:39+00:00

The callers of the functions performing irqtime kcpustat updates have
IRQS disabled, no need to disable them again.

Signed-off-by: Frederic Weisbecker 
Reviewed-by: Rik van Riel 
Cc: Eric Dumazet 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Link: http://lkml.kernel.org/r/1474849761-12678-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar

sched/irqtime: No need for preempt-safe accessors

2016-09-30T09:46:38+00:00

We can safely use the preempt-unsafe accessors for irqtime when we
flush its counters to kcpustat as IRQs are disabled at this time.

Signed-off-by: Frederic Weisbecker 
Reviewed-by: Rik van Riel 
Cc: Eric Dumazet 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Link: http://lkml.kernel.org/r/1474849761-12678-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar

sched/cputime: Improve scalability by not accounting thread group tasks pending runtime

2016-08-18T09:53:46+00:00

Commit:

  d670ec13178d0 ("posix-cpu-timers: Cure SMP wobbles")

started accounting thread group tasks pending runtime in thread_group_cputime().

Another commit:

  6e998916dfe32 ("sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency")

updated scheduler runtime statistics (call update_curr()) when reading task pending
runtime. Those changes cause bad performance of SYS_times() and
SYS_clock_gettimes(CLOCK_PROCESS_CPUTIME_ID) syscalls, especially on
larger systems with many CPUs.

While we would like to have cpuclock monotonicity kept i.e. have
problems fixed by above commits stay fixed, we also would like to have
good performance.

However when we notice that change from commit d670ec13178d0 is not
longer needed to solve problem addressed by that commit, because of
change from the second commit 6e998916dfe32, we can get room for
optimization. Since we update task while reading it's pending runtime
in task_sched_runtime(), clock_gettime(CLOCK_PROCESS_CPUTIME_ID) will
see updated values and on testcase from d670ec13178d0 process cpuclock
will not be smaller than thread cpuclock.

I tested the patch on testcases from commits d670ec13178d0,
6e998916dfe32 and some other cpuclock/cputimers testcases and
did not found cpuclock monotonicity problems or other malfunction.

This patch has the drawback that we will not provide thread group cputime
up-to-date to the last moment. For example when arming cputime timer,
we will arm it with possibly a bit outdated values and that timer will
trigger earlier compared to behaviour without the patch. However that
was the behaviour before d670ec13178d0 commit (kernel v3.1) so it's
unlikely to affect applications.

Patch improves related syscall performance, as measured by Giovanni's
benchmarks described in commit:

  6075620b0590e ("sched/cputime: Mitigate performance regression in times()/clock_gettime()")

The benchmark results are:

SYS_clock_gettime():

  threads    4.7-rc7     3.18-rc3              4.7-rc7 + prefetch    4.7-rc7 + patch
                         (pre-6e998916dfe3)
  2          3.48        2.23 ( 35.68%)        3.06 ( 11.83%)        1.08 ( 68.81%)
  5          3.33        2.83 ( 14.84%)        3.25 (  2.40%)        0.71 ( 78.55%)
  8          3.37        2.84 ( 15.80%)        3.26 (  3.30%)        0.56 ( 83.49%)
  12         3.32        3.09 (  6.69%)        3.37 ( -1.60%)        0.42 ( 87.28%)
  21         4.01        3.14 ( 21.70%)        3.90 (  2.74%)        0.35 ( 91.35%)
  30         3.63        3.28 (  9.75%)        3.36 (  7.41%)        0.28 ( 92.23%)
  48         3.71        3.02 ( 18.69%)        3.11 ( 16.27%)        0.39 ( 89.39%)
  79         3.75        2.88 ( 23.23%)        3.16 ( 15.74%)        0.46 ( 87.76%)
  110        3.81        2.95 ( 22.62%)        3.25 ( 14.80%)        0.56 ( 85.41%)
  128        3.88        3.05 ( 21.28%)        3.31 ( 14.76%)        0.62 ( 84.10%)

SYS_times():

  threads    4.7-rc7     3.18-rc3              4.7-rc7 + prefetch    4.7-rc7 + patch
                         (pre-6e998916dfe3)
  2          3.65        2.27 ( 37.94%)        3.25 ( 11.03%)        1.62 ( 55.71%)
  5          3.45        2.78 ( 19.34%)        3.17 (  7.92%)        2.33 ( 32.28%)
  8          3.52        2.79 ( 20.66%)        3.22 (  8.69%)        2.06 ( 41.44%)
  12         3.29        3.02 (  8.33%)        3.36 ( -2.04%)        2.00 ( 39.18%)
  21         4.07        3.10 ( 23.86%)        3.92 (  3.78%)        2.07 ( 49.18%)
  30         3.87        3.33 ( 13.80%)        3.40 ( 12.17%)        1.89 ( 51.12%)
  48         3.79        2.96 ( 21.94%)        3.16 ( 16.61%)        1.69 ( 55.46%)
  79         3.88        2.88 ( 25.82%)        3.28 ( 15.42%)        1.60 ( 58.81%)
  110        3.90        2.98 ( 23.73%)        3.38 ( 13.35%)        1.73 ( 55.61%)
  128        4.00        3.10 ( 22.40%)        3.38 ( 15.45%)        1.66 ( 58.52%)

Reported-and-tested-by: Giovanni Gherdovich 
Signed-off-by: Stanislaw Gruszka 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Mike Galbraith 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Link: http://lkml.kernel.org/r/20160817093043.GA25206@redhat.com
Signed-off-by: Ingo Molnar

sched/cputime: Resync steal time when guest & host lose sync

2016-08-18T09:19:48+00:00

Commit:

  57430218317e ("sched/cputime: Count actually elapsed irq & softirq time")

... fixed a bug but also triggered a regression:

On an i5 laptop, 4 pCPUs, 4vCPUs for one full dynticks guest, there are four
CPU hog processes(for loop) running in the guest, I hot-unplug the pCPUs
on host one by one until there is only one left, then observe CPU utilization
via 'top' in the guest, it shows:

  100% st for cpu0(housekeeping)
   75% st for other CPUs (nohz full mode)

However, w/o this commit it shows the correct 75% for all four CPUs.

When a guest is interrupted for a longer amount of time, missed clock ticks
are not redelivered later. Because of that, we should not limit the amount
of steal time accounted to the amount of time that the calling functions
think have passed.

However, the interval returned by account_other_time() is NOT rounded down
to the nearest jiffy, while the base interval in get_vtime_delta() it is
subtracted from is, so the max cputime limit is required to avoid underflow.

This patch fixes the regression by limiting the account_other_time() from
get_vtime_delta() to avoid underflow, and lets the other three call sites
(in account_other_time() and steal_account_process_time()) account however
much steal time the host told us elapsed.

Suggested-by: Rik van Riel 
Suggested-by: Paolo Bonzini 
Signed-off-by: Wanpeng Li 
Reviewed-by: Rik van Riel 
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Radim Krcmar 
Cc: Thomas Gleixner 
Cc: kvm@vger.kernel.org
Link: http://lkml.kernel.org/r/1471399546-4069-1-git-send-email-wanpeng.li@hotmail.com
[ Improved the changelog. ]
Signed-off-by: Ingo Molnar

sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression

2016-08-18T08:48:46+00:00

Mike reports:

 Roughly 10% of the time, ltp testcase getrusage04 fails:
 getrusage04    0  TINFO  :  Expected timers granularity is 4000 us
 getrusage04    0  TINFO  :  Using 1 as multiply factor for max [us]time increment (1000+4000us)!
 getrusage04    0  TINFO  :  utime:           0us; stime:         179us
 getrusage04    0  TINFO  :  utime:        3751us; stime:           0us
 getrusage04    1  TFAIL  :  getrusage04.c:133: stime increased > 5000us:

And tracked it down to the case where the task simply doesn't get
_any_ [us]time ticks.

Update the code to assume all rtime is utime when we lack information,
thus ensuring a task that elides the tick gets time accounted.

Reported-by: Mike Galbraith 
Tested-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Frederic Weisbecker 
Cc: Fredrik Markstrom 
Cc: Linus Torvalds 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Radim 
Cc: Rik van Riel 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: Wanpeng Li 
Cc: stable@vger.kernel.org # 4.3+
Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime")
Signed-off-by: Ingo Molnar

sched/cputime: Fix omitted ticks passed in parameter

2016-08-11T14:34:37+00:00

Commit:

  f9bcf1e0e014 ("sched/cputime: Fix steal time accounting")

... fixes a leak on steal time accounting but forgets to account
the ticks passed in parameters, assuming there is only one to
take into account.

Let's consider that parameter back.

Signed-off-by: Frederic Weisbecker 
Acked-by: Wanpeng Li 
Cc: Linus Torvalds 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra 
Cc: Radim 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Cc: linux-tip-commits@vger.kernel.org
Link: http://lkml.kernel.org/r/20160811125822.GB4214@lerouge
Signed-off-by: Ingo Molnar

sched/cputime: Fix steal time accounting

2016-08-11T09:02:14+00:00

Commit:

  57430218317 ("sched/cputime: Count actually elapsed irq & softirq time")

... didn't take steal time into consideration with passing the noirqtime
kernel parameter.

As Paolo pointed out before:

| Why not? If idle=poll, for example, any time the guest is suspended (and
| thus cannot poll) does count as stolen time.

This patch fixes it by reducing steal time from idle time accounting when
the noirqtime parameter is true. The average idle time drops from 56.8%
to 54.75% for nohz idle kvm guest(noirqtime, idle=poll, four vCPUs running
on one pCPU).

Signed-off-by: Wanpeng Li 
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Paolo Bonzini 
Cc: Peter Zijlstra (Intel) 
Cc: Peter Zijlstra 
Cc: Radim 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1470893795-3527-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar

Merge tag 'for-linus-4.8-rc0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

2016-07-27T18:35:37+00:00

Pull xen updates from David Vrabel:
 "Features and fixes for 4.8-rc0:

   - ACPI support for guests on ARM platforms.
   - Generic steal time support for arm and x86.
   - Support cases where kernel cpu is not Xen VCPU number (e.g., if
     in-guest kexec is used).
   - Use the system workqueue instead of a custom workqueue in various
     places"

* tag 'for-linus-4.8-rc0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip: (47 commits)
  xen: add static initialization of steal_clock op to xen_time_ops
  xen/pvhvm: run xen_vcpu_setup() for the boot CPU
  xen/evtchn: use xen_vcpu_id mapping
  xen/events: fifo: use xen_vcpu_id mapping
  xen/events: use xen_vcpu_id mapping in events_base
  x86/xen: use xen_vcpu_id mapping when pointing vcpu_info to shared_info
  x86/xen: use xen_vcpu_id mapping for HYPERVISOR_vcpu_op
  xen: introduce xen_vcpu_id mapping
  x86/acpi: store ACPI ids from MADT for future usage
  x86/xen: update cpuid.h from Xen-4.7
  xen/evtchn: add IOCTL_EVTCHN_RESTRICT
  xen-blkback: really don't leak mode property
  xen-blkback: constify instance of "struct attribute_group"
  xen-blkfront: prefer xenbus_scanf() over xenbus_gather()
  xen-blkback: prefer xenbus_scanf() over xenbus_gather()
  xen: support runqueue steal time on xen
  arm/xen: add support for vm_assist hypercall
  xen: update xen headers
  xen-pciback: drop superfluous variables
  xen-pciback: short-circuit read path used for merging write values
  ...