Hi Chris
On Sat, 24 Oct 2020 at 01:49, Chris Mason <clm@xxxxxx> wrote:
Hi everyone,
We’re validating a new kernel in the fleet, and compared with v5.2,
Which version are you using ?
several improvements have been added since v5.5 and the rework of load_balance
performance is ~2-3% lower for some of our workloads. After some
digging, Johannes found that our involuntary context switch rate was ~2x
higher, and we were leaving a CPU idle a higher percentage of the time,
even though the workload was trying to saturate the system.
We were able to reproduce the problem with schbench, and Johannes
bisected down to:
commit 0b0695f2b34a4afa3f6e9aa1ff0e5336d8dad912
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date: Fri Oct 18 15:26:31 2019 +0200
sched/fair: Rework load_balance()
Our working theory is the load balancing changes are leaving processes
behind busy CPUs instead of moving them onto idle ones. I made a few
schbench modifications to make this easier to demonstrate:
https://git.kernel.org/pub/scm/linux/kernel/git/mason/schbench.git/
My VM has 40 cpus (20 cores, 2 threads per core), and my schbench
command line is:
What is the topology ? are they all part of the same LLC ?