On 2/7/2024 10:12 AM, Andrea Righi wrote:
> On Wed, Feb 07, 2024 at 02:04:12PM +0100, Uladzislau Rezki wrote:
>>>>
>>>> I repeated some tests in a more isolated environment and posted the
>>>> results here:
>>>> https://discourse.ubuntu.com/t/enable-low-latency-features-in-the-generic-ubuntu-kernel-for-24-04/42255
>>>>
>>>> Highlights:
>>>>
>>>> - stress-ng --matrix seems quite unpredictable to be used a benchmarks
>>>> in this scenario (the bogo-ops/s are very susceptible to any kind of
>>>> interference, so even if in the long runs NO_HZ_FULL still seems to
>>>> provide some benefits looking at the average, we also need to
>>>> consider that there might be a significant error in the measurements,
>>>> standard deviation was pretty high)
>>>>
>>>> - fio doing short writes (in page cache) seems to perform like 2x
>>>> better in terms of iops with nohz_full, respect to the other cases
>>>> and it performs 2x slower with large IO writes (not sure why... need
>>>> to investigate more)
>>>>
>>>> - with lazy RCU enabled hrtimer_interrupt() takes like 2x more to
>>>> return, respect to the other cases (is this expected?)
>>>
>>> This last is surprising at first glance, but I could be missing
>>> something. Joel, Uladzislau, thoughts?
>>>
>> Could you please share the steps how you run "fio" tests?
>
> For short writes I was running something like this (on a 8 cores system):
>
> $ fio --rw=write --bs=1M --size=32M --numjobs=8 --name=worker --time_based
> --runtime=300
>
> Larger writes:
>
> $ fio --rw=write --bs=1M --size=1G --numjobs=8 --name=worker --time_based
> --runtime=300
Andrea, Thank you for providing these to us!
- Joel
