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Srikar Dronamraju 04a2096c4b powerpc/vcpu: Assume dedicated processors as non-preempt 
commit 14c73bd344 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 12:17:23 +01:00
..
cmm.c powerpc/pseries/cmm: Implement release() function for sysfs device 2020-01-04 19:12:54 +01:00
dlpar.c powerpc/pseries/dlpar: Fix a missing check in dlpar_parse_cc_property() 2019-12-05 09:21:23 +01:00
dtl.c powerpc/pseries: Fix how we iterate over the DTL entries 2019-11-24 08:19:53 +01:00
eeh_pseries.c powerpc/eeh: Add EEH operations to notify resume 2018-01-27 20:02:52 +11:00
event_sources.c powerpc: Convert to using %pOF instead of full_name 2017-08-23 22:27:04 +10:00
firmware.c powerpc/firmware: Add definitions for new drc-info firmware feature 2018-01-21 16:21:40 +11:00
hotplug-cpu.c powerpc/pseries: Perform full re-add of CPU for topology update post-migration 2019-04-05 22:33:13 +02:00
hotplug-memory.c powerpc/pseries: Fix node leak in update_lmb_associativity_index() 2019-12-05 09:20:47 +01:00
hvCall.S jump_label: move 'asm goto' support test to Kconfig 2019-06-04 08:02:34 +02:00
hvCall_inst.c powerpc/pseries: hcall_exit tracepoint retval should be signed 2018-05-10 23:17:43 +10:00
hvconsole.c powerpc/pseries/hvconsole: Fix stack overread via udbg 2020-01-09 10:19:08 +01:00
hvcserver.c powerpc/pseries/hvcserver: don't memset pi_buff if it is null 2015-10-09 08:03:03 +11:00
ibmebus.c powerpc: Use octal numbers for file permissions 2018-01-22 05:48:33 +11:00
io_event_irq.c powerpc: Various typo fixes 2016-06-14 13:58:26 +10:00
iommu.c powerpc updates for 4.16 2018-02-02 10:01:04 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kexec.c powerpc/xive: Remove xive_kexec_teardown_cpu() 2018-08-07 21:49:28 +10:00
lpar.c powerpc/pseries: Export raw per-CPU VPA data via debugfs 2019-12-01 09:16:44 +01:00
lparcfg.c powerpc/pseries: lparcfg calculate PURR on demand 2018-06-03 20:40:27 +10:00
Makefile powerpc/Makefiles: Convert ifeq to ifdef where possible 2018-08-08 00:32:36 +10:00
mobility.c powerpc/pseries/mobility: use cond_resched when updating device tree 2019-10-07 18:56:50 +02:00
msi.c powerpc/pci: Remove OF node back pointer from pci_dn 2017-08-31 14:26:12 +10:00
nvram.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
of_helpers.c pseries/drc-info: Search DRC properties for CPU indexes 2018-01-21 16:21:46 +11:00
of_helpers.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
offline_states.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci.c powerpc/pseries/pci: Associate PEs to VFs in configure SR-IOV 2018-01-27 20:02:53 +11:00
pci_dlpar.c powerpc: Convert to using %pOF instead of full_name 2017-08-23 22:27:04 +10:00
power.c powerpc/sparse: Include headers containing prototypes 2016-06-16 22:40:19 +10:00
pseries.h powerpc/rfi-flush: Call setup_rfi_flush() after LPM migration 2018-03-27 19:25:14 +11:00
pseries_energy.c powerpc/pseries/energy: Use OF accessor functions to read ibm,drc-indexes 2019-04-03 06:26:29 +02:00
ras.c powerpc/pseries: Fix endianness while restoring of r3 in MCE handler. 2018-08-10 22:12:34 +10:00
reconfig.c powerpc: Use octal numbers for file permissions 2018-01-22 05:48:33 +11:00
rng.c
scanlog.c powerpc: Use octal numbers for file permissions 2018-01-22 05:48:33 +11:00
setup.c powerpc/vcpu: Assume dedicated processors as non-preempt 2020-01-12 12:17:23 +01:00
smp.c Merge branch 'topic/paca' into next 2018-03-31 09:09:36 +11:00
suspend.c powerpc: Use octal numbers for file permissions 2018-01-22 05:48:33 +11:00
vio.c powerpc: rename dma_direct_ to dma_nommu_ 2018-01-10 16:41:14 +01:00