[LibreQoS] Fwd: [PATCH v2 0/4] cpumask: improve on cpumask_local_spread() locality

[Dave Taht]

---------- Forwarded message ---------
From: Yury Norov <yury.norov at gmail.com>
Date: Sat, Nov 12, 2022 at 11:14 AM
Subject: [PATCH v2 0/4] cpumask: improve on cpumask_local_spread() locality
To: <linux-kernel at vger.kernel.org>, David S. Miller
<davem at davemloft.net>, Andy Shevchenko
<andriy.shevchenko at linux.intel.com>, Barry Song <baohua at kernel.org>,
Ben Segall <bsegall at google.com>, haniel Bristot de Oliveira
<bristot at redhat.com>, Dietmar Eggemann <dietmar.eggemann at arm.com>, Gal
Pressman <gal at nvidia.com>, Greg Kroah-Hartman
<gregkh at linuxfoundation.org>, Heiko Carstens <hca at linux.ibm.com>, Ingo
Molnar <mingo at redhat.com>, Jakub Kicinski <kuba at kernel.org>, Jason
Gunthorpe <jgg at nvidia.com>, Jesse Brandeburg
<jesse.brandeburg at intel.com>, Jonathan Cameron
<Jonathan.Cameron at huawei.com>, Juri Lelli <juri.lelli at redhat.com>,
Leon Romanovsky <leonro at nvidia.com>, Mel Gorman <mgorman at suse.de>,
Peter Zijlstra <peterz at infradead.org>, Rasmus Villemoes
<linux at rasmusvillemoes.dk>, Saeed Mahameed <saeedm at nvidia.com>, Steven
Rostedt <rostedt at goodmis.org>, Tariq Toukan <tariqt at nvidia.com>, Tariq
Toukan <ttoukan.linux at gmail.com>, Tony Luck <tony.luck at intel.com>,
Valentin Schneider <vschneid at redhat.com>, Vincent Guittot
<vincent.guittot at linaro.org>
Cc: Yury Norov <yury.norov at gmail.com>, <linux-crypto at vger.kernel.org>,
<netdev at vger.kernel.org>, <linux-rdma at vger.kernel.org>


cpumask_local_spread() currently checks local node for presence of i'th
CPU, and then if it finds nothing makes a flat search among all non-local
CPUs. We can do it better by checking CPUs per NUMA hops.

This series is inspired by Tariq Toukan and Valentin Schneider's "net/mlx5e:
Improve remote NUMA preferences used for the IRQ affinity hints"

https://patchwork.kernel.org/project/netdevbpf/patch/20220728191203.4055-3-tariqt@nvidia.com/

According to their measurements, for mlx5e:

        Bottleneck in RX side is released, reached linerate (~1.8x speedup).
        ~30% less cpu util on TX.

This patch makes cpumask_local_spread() traversing CPUs based on NUMA
distance, just as well, and I expect comparabale improvement for its
users, as in case of mlx5e.

I tested new behavior on my VM with the following NUMA configuration:

root at debian:~# numactl -H
available: 4 nodes (0-3)
node 0 cpus: 0 1 2 3
node 0 size: 3869 MB
node 0 free: 3740 MB
node 1 cpus: 4 5
node 1 size: 1969 MB
node 1 free: 1937 MB
node 2 cpus: 6 7
node 2 size: 1967 MB
node 2 free: 1873 MB
node 3 cpus: 8 9 10 11 12 13 14 15
node 3 size: 7842 MB
node 3 free: 7723 MB
node distances:
node   0   1   2   3
  0:  10  50  30  70
  1:  50  10  70  30
  2:  30  70  10  50
  3:  70  30  50  10

And the cpumask_local_spread() for each node and offset traversing looks
like this:

node 0:   0   1   2   3   6   7   4   5   8   9  10  11  12  13  14  15
node 1:   4   5   8   9  10  11  12  13  14  15   0   1   2   3   6   7
node 2:   6   7   0   1   2   3   8   9  10  11  12  13  14  15   4   5
node 3:   8   9  10  11  12  13  14  15   4   5   6   7   0   1   2   3

v1: https://lore.kernel.org/lkml/20221111040027.621646-5-yury.norov@gmail.com/T/
v2:
 - use bsearch() in sched_numa_find_nth_cpu();
 - fix missing 'static inline' in 3rd patch.

Yury Norov (4):
  lib/find: introduce find_nth_and_andnot_bit
  cpumask: introduce cpumask_nth_and_andnot
  sched: add sched_numa_find_nth_cpu()
  cpumask: improve on cpumask_local_spread() locality

 include/linux/cpumask.h  | 20 +++++++++++++++
 include/linux/find.h     | 33 ++++++++++++++++++++++++
 include/linux/topology.h |  8 ++++++
 kernel/sched/topology.c  | 55 ++++++++++++++++++++++++++++++++++++++++
 lib/cpumask.c            | 12 ++-------
 lib/find_bit.c           |  9 +++++++
 6 files changed, 127 insertions(+), 10 deletions(-)

--
2.34.1



-- 
This song goes out to all the folk that thought Stadia would work:
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Dave Täht CEO, TekLibre, LLC