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Filename Latest commit message Latest commit date
Srikar Dronamraju 1e8a2bfed0 powerpc/vcpu: Assume dedicated processors as non-preempt 
commit 14c73bd344da60abaf7da3ea2e7733ddda35bbac upstream.

With commit 247f2f6f3c ("sched/core: Don't schedule threads on
pre-empted vCPUs"), the scheduler avoids preempted vCPUs to schedule
tasks on wakeup. This leads to wrong choice of CPU, which in-turn
leads to larger wakeup latencies. Eventually, it leads to performance
regression in latency sensitive benchmarks like soltp, schbench etc.

On Powerpc, vcpu_is_preempted() only looks at yield_count. If the
yield_count is odd, the vCPU is assumed to be preempted. However
yield_count is increased whenever the LPAR enters CEDE state (idle).
So any CPU that has entered CEDE state is assumed to be preempted.

Even if vCPU of dedicated LPAR is preempted/donated, it should have
right of first-use since they are supposed to own the vCPU.

On a Power9 System with 32 cores:
  # lscpu
  Architecture:        ppc64le
  Byte Order:          Little Endian
  CPU(s):              128
  On-line CPU(s) list: 0-127
  Thread(s) per core:  8
  Core(s) per socket:  1
  Socket(s):           16
  NUMA node(s):        2
  Model:               2.2 (pvr 004e 0202)
  Model name:          POWER9 (architected), altivec supported
  Hypervisor vendor:   pHyp
  Virtualization type: para
  L1d cache:           32K
  L1i cache:           32K
  L2 cache:            512K
  L3 cache:            10240K
  NUMA node0 CPU(s):   0-63
  NUMA node1 CPU(s):   64-127

  # perf stat -a -r 5 ./schbench
  v5.4                               v5.4 + patch
  Latency percentiles (usec)         Latency percentiles (usec)
        50.0000th: 45                      50.0th: 45
        75.0000th: 62                      75.0th: 63
        90.0000th: 71                      90.0th: 74
        95.0000th: 77                      95.0th: 78
        *99.0000th: 91                     *99.0th: 82
        99.5000th: 707                     99.5th: 83
        99.9000th: 6920                    99.9th: 86
        min=0, max=10048                   min=0, max=96
  Latency percentiles (usec)         Latency percentiles (usec)
        50.0000th: 45                      50.0th: 46
        75.0000th: 61                      75.0th: 64
        90.0000th: 72                      90.0th: 75
        95.0000th: 79                      95.0th: 79
        *99.0000th: 691                    *99.0th: 83
        99.5000th: 3972                    99.5th: 85
        99.9000th: 8368                    99.9th: 91
        min=0, max=16606                   min=0, max=117
  Latency percentiles (usec)         Latency percentiles (usec)
        50.0000th: 45                      50.0th: 46
        75.0000th: 61                      75.0th: 64
        90.0000th: 71                      90.0th: 75
        95.0000th: 77                      95.0th: 79
        *99.0000th: 106                    *99.0th: 83
        99.5000th: 2364                    99.5th: 84
        99.9000th: 7480                    99.9th: 90
        min=0, max=10001                   min=0, max=95
  Latency percentiles (usec)         Latency percentiles (usec)
        50.0000th: 45                      50.0th: 47
        75.0000th: 62                      75.0th: 65
        90.0000th: 72                      90.0th: 75
        95.0000th: 78                      95.0th: 79
        *99.0000th: 93                     *99.0th: 84
        99.5000th: 108                     99.5th: 85
        99.9000th: 6792                    99.9th: 90
        min=0, max=17681                   min=0, max=117
  Latency percentiles (usec)         Latency percentiles (usec)
        50.0000th: 46                      50.0th: 45
        75.0000th: 62                      75.0th: 64
        90.0000th: 73                      90.0th: 75
        95.0000th: 79                      95.0th: 79
        *99.0000th: 113                    *99.0th: 82
        99.5000th: 2724                    99.5th: 83
        99.9000th: 6184                    99.9th: 93
        min=0, max=9887                    min=0, max=111

   Performance counter stats for 'system wide' (5 runs):

  context-switches    43,373  ( +-  0.40% )   44,597 ( +-  0.55% )
  cpu-migrations       1,211  ( +-  5.04% )      220 ( +-  6.23% )
  page-faults         15,983  ( +-  5.21% )   15,360 ( +-  3.38% )

Waiman Long suggested using static_keys.

Fixes: 247f2f6f3c ("sched/core: Don't schedule threads on pre-empted vCPUs")
Cc: stable@vger.kernel.org # v4.18+
Reported-by: Parth Shah <parth@linux.ibm.com>
Reported-by: Ihor Pasichnyk <Ihor.Pasichnyk@ibm.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
Tested-by: Parth Shah <parth@linux.ibm.com>
[mpe: Move the key and setting of the key to pseries/setup.c]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191213035036.6913-1-mpe@ellerman.id.au
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-01-12 12:21:29 +01:00
arch powerpc/vcpu: Assume dedicated processors as non-preempt 2020-01-12 12:21:29 +01:00
block compat_ioctl: block: handle BLKGETZONESZ/BLKGETNRZONES 2020-01-09 10:19:58 +01:00
certs
crypto KEYS: asymmetric: return ENOMEM if akcipher_request_alloc() fails 2019-12-31 16:46:07 +01:00
Documentation dt-bindings: clock: renesas: rcar-usb2-clock-sel: Fix typo in example 2020-01-09 10:20:05 +01:00
drivers pinctrl: pinmux: fix a possible null pointer in pinmux_can_be_used_for_gpio 2020-01-12 12:21:28 +01:00
fs Btrfs: fix cloning range with a hole when using the NO_HOLES feature 2020-01-12 12:21:29 +01:00
include netfilter: uapi: Avoid undefined left-shift in xt_sctp.h 2020-01-12 12:21:17 +01:00
init
ipc
kernel locking/spinlock/debug: Fix various data races 2020-01-12 12:21:13 +01:00
lib lib/ubsan: don't serialize UBSAN report 2020-01-09 10:20:07 +01:00
LICENSES
mm mm/hugetlb: defer freeing of huge pages if in non-task context 2020-01-09 10:20:07 +01:00
net cfg80211: fix double-free after changing network namespace 2020-01-12 12:21:28 +01:00
samples samples: bpf: fix syscall_tp due to unused syscall 2020-01-12 12:21:26 +01:00
scripts gcc-plugins: make it possible to disable CONFIG_GCC_PLUGINS again 2020-01-09 10:19:57 +01:00
security apparmor: fix aa_xattrs_match() may sleep while holding a RCU lock 2020-01-09 10:20:00 +01:00
sound ASoC: SOF: Intel: split cht and byt debug window sizes 2020-01-12 12:21:22 +01:00
tools kselftest: Support old perl versions 2020-01-12 12:21:26 +01:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-09 10:20:00 +01:00
virt KVM: arm/arm64: Properly handle faulting of device mappings 2019-12-31 16:46:24 +01:00
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MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-11-22 14:28:14 -08:00
Makefile Linux 5.4.10 2020-01-09 10:25:53 +01:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.