Re: [PATCH 4/4] sched/fair: Proportional newidle balance

["Mohamed Abuelfotoh, Hazem" <abuehaze@amazon.com>]

On 04/02/2026 14:05, Peter Zijlstra wrote:

>> I will try to
>> come-up with standalone reproduction steps that can be used to investigate
>> this memcached regression. Meanwhile we will share the fio regression
>> reproduction steps that I mentioned in my previous update. This should be
>> much simpler in steps and can be done on a single machine.
> 
> Thanks! I have a few machines with a 'spare' nvme drive to run things
> on, hopefully that is sufficient.

It looks like the previously reported fio regression has been fully 
mitigated by the proposed patch [1]. I verified this on both 6.18.5 & 
6.12.66. I will try to come-up with standalone reproduction for the 
memcached regression to make it easier for debugging.


**fio regression reproduction environment**

AWS EC2 instance: c5ad.24xlarge

96 vCPUs = 48 Cores with HT
12 CCDs
Memory : 192 GiB
SSD Disk space: 1900 GiB
SSD Disk Max write IOPS: 180K
SSD Disk Max Write B.W: 760 MB/sec

Below are the results of three different runs.

6.18.5

6.18.5_revert 6.18.5 with the revert of 1b9c118fe318 ("sched/fair: 
Proportional newidle balance")

6.18.5_proposed 6.18.5 with patch[1]

---------------------------------------------------------------

Version 6.18.5

# sudo fio --time_based --name=benchmark --size=50G --runtime=60 
--filename=/dev/nvme1n1 --ioengine=psync --randrepeat=0 --iodepth=1 
--fsync=64 --invalidate=1 --verify=0 --verify_fatal=0 --blocksize=4k 
--group_reporting --rw=randwrite --numjobs=4

Run status group 0 (all jobs):
   WRITE: bw=478MiB/s (501MB/s), 478MiB/s-478MiB/s (501MB/s-501MB/s), 
io=28.0GiB (30.1GB), run=60003-60003msec

----------------------------------------------------------------

Version 6.18.5_revert

# sudo fio --time_based --name=benchmark --size=50G --runtime=60 
--filename=/dev/nvme1n1 --ioengine=psync --randrepeat=0 --iodepth=1 
--fsync=64 --invalidate=1 --verify=0 --verify_fatal=0 --blocksize=4k 
--group_reporting --rw=randwrite --numjobs=4

Run status group 0 (all jobs):
   WRITE: bw=549MiB/s (575MB/s), 549MiB/s-549MiB/s (575MB/s-575MB/s), 
io=32.2GiB (34.5GB), run=60002-60002msec

-----------------------------------------------------------------

Version 6.18.5_proposed

# sudo fio --time_based --name=benchmark --size=50G --runtime=60 
--filename=/dev/nvme1n1 --ioengine=psync --randrepeat=0 --iodepth=1 
--fsync=64 --invalidate=1 --verify=0 --verify_fatal=0 --blocksize=4k 
--group_reporting --rw=randwrite --numjobs=4

Run status group 0 (all jobs):
   WRITE: bw=551MiB/s (578MB/s), 551MiB/s-551MiB/s (578MB/s-578MB/s), 
io=32.3GiB (34.7GB), run=60003-60003msec


[1] 
https://lore.kernel.org/all/20260127151748.GA1079264@noisy.programming.kicks-ass.net/T/#u