Re: [PATCH v2 00/23] Cache aware scheduling

[Aaron Lu]

On Wed, Dec 03, 2025 at 03:07:19PM -0800, Tim Chen wrote:
... ...
> Test results:
> 
> The patch series was applied and tested on v6.18-rc7.
> See: https://github.com/timcchen1298/linux/commits/cache_aware_v2
> 
> The first test platform is a 2 socket Intel Sapphire Rapids with 30
> cores per socket. The DRAM interleaving is enabled in the BIOS so it
> essential has one NUMA node with two last level caches. There are 60
> CPUs associated with each last level cache.
> 
> The second test platform is a AMD Genoa. There are 4 Nodes and 32 CPUs
> per node. Each node has 2 CCXs and each CCX has 16 CPUs.
> 
> hackbench/schbench/netperf/stream/stress-ng/chacha20 were launched on
> these two platforms.
> 
> [TL;DR]
> Sappire Rapids:
> hackbench shows significant improvement when the number of
> different active threads is below the capacity of a LLC.
> schbench shows overall wakeup latency improvement.
> ChaCha20-xiangshan shows good throughput improvement.
> 
> Genoa:
> ChaCha20-xiangshan shows huge throughput improvement.
> No obvious difference is observed in hackbench/schbench

I think for small task number hackbench run, there should be some
improvement.

I tried thread/pipe/2fds/1group, i.e. 4 tasks on Genoa:
./hackbench -T -f 2 -g 1 -p -l 2000000
And I noticed performance improved a lot:
(Result in seconds, less is better)

       llc_off       llc_on          diff
time   4.755±1.6%    2.684±6.25%    +43.6%

llc_off means /sys/kernel/debug/sched/llc_enabled set to 0 while
llc_on means /sys/kernel/debug/sched/llc_enabled set to 1, other
tunnables are left unchanged.
Turbo is disabled and cpufreq set to performance.

I also tried redis and noticed when I set io-threads to 4 in redis.conf,
there is also some improvement on AMD Genoa:

                 llc_off        manual      diff     llc_on      diff
throughput      1536727±0%     1737619±0%  +13.1%   1737720±0%  +13.1%

Client cmdline:
numactl -N 1 redis-benchmark --threads 4 -t set -r 100000 -P 16 -n 10000000
server cmdline: numactl -N 0 redis-server ./redis.conf
I also tried to manually bind all tasks of redis server to a single LLC
to see if this workload benefits from aggregation and that's what manual
means: taskset -c 8-15,200-207 redis-server ./redis.conf

According to the result, I think this 'cache aware scheduling' works
as expected in that its performance is the same as manual binding; and
they all beat llc_off.