[PATCH v2 0/4] Powerpc: Better preemption for shared processor

[Srikar Dronamraju]

Currently, vcpu_is_preempted will return the yield_count for
shared_processor. On a PowerVM LPAR, Phyp schedules at SMT8 core boundary
i.e all CPUs belonging to a core are either group scheduled in or group
scheduled out. This can be used to better predict non-preempted CPUs on
PowerVM shared LPARs.

perf stat -r 5 -a perf bench sched pipe -l 10000000 (lesser time is better)

powerpc/next
     35,107,951.20 msec cpu-clock                 #  255.898 CPUs utilized            ( +-  0.31% )
        23,655,348      context-switches          #    0.674 K/sec                    ( +-  3.72% )
            14,465      cpu-migrations            #    0.000 K/sec                    ( +-  5.37% )
            82,463      page-faults               #    0.002 K/sec                    ( +-  8.40% )
 1,127,182,328,206      cycles                    #    0.032 GHz                      ( +-  1.60% )  (66.67%)
    78,587,300,622      stalled-cycles-frontend   #    6.97% frontend cycles idle     ( +-  0.08% )  (50.01%)
   654,124,218,432      stalled-cycles-backend    #   58.03% backend cycles idle      ( +-  1.74% )  (50.01%)
   834,013,059,242      instructions              #    0.74  insn per cycle
                                                  #    0.78  stalled cycles per insn  ( +-  0.73% )  (66.67%)
   132,911,454,387      branches                  #    3.786 M/sec                    ( +-  0.59% )  (50.00%)
     2,890,882,143      branch-misses             #    2.18% of all branches          ( +-  0.46% )  (50.00%)

           137.195 +- 0.419 seconds time elapsed  ( +-  0.31% )

powerpc/next + patchset
     29,981,702.64 msec cpu-clock                 #  255.881 CPUs utilized            ( +-  1.30% )
        40,162,456      context-switches          #    0.001 M/sec                    ( +-  0.01% )
             1,110      cpu-migrations            #    0.000 K/sec                    ( +-  5.20% )
            62,616      page-faults               #    0.002 K/sec                    ( +-  3.93% )
 1,430,030,626,037      cycles                    #    0.048 GHz                      ( +-  1.41% )  (66.67%)
    83,202,707,288      stalled-cycles-frontend   #    5.82% frontend cycles idle     ( +-  0.75% )  (50.01%)
   744,556,088,520      stalled-cycles-backend    #   52.07% backend cycles idle      ( +-  1.39% )  (50.01%)
   940,138,418,674      instructions              #    0.66  insn per cycle
                                                  #    0.79  stalled cycles per insn  ( +-  0.51% )  (66.67%)
   146,452,852,283      branches                  #    4.885 M/sec                    ( +-  0.80% )  (50.00%)
     3,237,743,996      branch-misses             #    2.21% of all branches          ( +-  1.18% )  (50.01%)

            117.17 +- 1.52 seconds time elapsed  ( +-  1.30% )

This is around 14.6% improvement in performance.

Changelog:
v1->v2:
v1: https://lore.kernel.org/linuxppc-dev/20201028123512.871051-1-srikar@linux.vnet.ibm.com/t/#u
 - Rebased to 27th Nov linuxppc/merge tree.
 - Moved a hunk to fix a no previous prototype warning reported by: lkp at intel.com
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/thread/C6PTRPHWMC7VV4OTYN3ISYKDHTDQS6YI/

Cc: linuxppc-dev <linuxppc-dev at lists.ozlabs.org>
Cc: LKML <linux-kernel at vger.kernel.org>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Nicholas Piggin <npiggin at gmail.com>
Cc: Nathan Lynch <nathanl at linux.ibm.com>
Cc: Gautham R Shenoy <ego at linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Valentin Schneider <valentin.schneider at arm.com>
Cc: Juri Lelli <juri.lelli at redhat.com>
Cc: Waiman Long <longman at redhat.com>
Cc: Phil Auld <pauld at redhat.com>

Srikar Dronamraju (4):
  powerpc: Refactor is_kvm_guest declaration to new header
  powerpc: Rename is_kvm_guest to check_kvm_guest
  powerpc: Reintroduce is_kvm_guest
  powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted

 arch/powerpc/include/asm/firmware.h  |  6 ------
 arch/powerpc/include/asm/kvm_guest.h | 25 +++++++++++++++++++++++++
 arch/powerpc/include/asm/kvm_para.h  |  2 +-
 arch/powerpc/include/asm/paravirt.h  | 18 ++++++++++++++++++
 arch/powerpc/kernel/firmware.c       |  5 ++++-
 arch/powerpc/platforms/pseries/smp.c |  3 ++-
 6 files changed, 50 insertions(+), 9 deletions(-)
 create mode 100644 arch/powerpc/include/asm/kvm_guest.h

-- 
2.18.4