lkml.org 
[lkml]   [2020]   [Oct]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 0/4] Powerpc: Better preemption for shared processor
From
Date
On 10/28/20 8:35 AM, Srikar Dronamraju wrote:
> 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.
>
> Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> Cc: LKML <linux-kernel@vger.kernel.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Nathan Lynch <nathanl@linux.ibm.com>
> Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Phil Auld <pauld@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
>
This patch series looks good to me and the performance is nice too.

Acked-by: Waiman Long <longman@redhat.com>

Just curious, is the performance mainly from the use of static_branch
(patches 1 - 3) or from reducing call to yield_count_of().

Cheers,
Longman

\
 
 \ /
  Last update: 2020-10-29 01:02    [W:0.056 / U:0.936 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site