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SubjectRe: [REGRESSION] 5-10% increase in IO latencies with nohz balance patch
Date

Hi,

On 22/12/21 13:42, Thorsten Leemhuis wrote:
> What's the status here? Just wondering, because there hasn't been any
> activity in this thread since 11 days and the festive season is upon us.
>
> Was the discussion moved elsewhere? Or is this still a mystery? And if
> it is: how bad is it, does it need to be fixed before Linus releases 5.16?
>

I got to the end of bisect #3 yesterday, the incriminated commit doesn't
seem to make much sense but I've just re-tested it and there is a clear
regression between that commit and its parent (unlike bisect #1 and #2):

2127d22509aec3a83dffb2a3c736df7ba747a7ce mm, slub: fix two bugs in slab_debug_trace_open()
write_clat_ns_p99 195395.92 199638.20 4797.01 2.17%
write_iops 17305.79 17188.24 250.66 -0.68%

write_clat_ns_p99 195543.84 199996.70 5122.88 2.28%
write_iops 17300.61 17241.86 251.56 -0.34%

write_clat_ns_p99 195543.84 200724.48 5122.88 2.65%
write_iops 17300.61 17246.63 251.56 -0.31%

write_clat_ns_p99 195543.84 200445.41 5122.88 2.51%
write_iops 17300.61 17215.47 251.56 -0.49%

6d2aec9e123bb9c49cb5c7fc654f25f81e688e8c mm/mempolicy: do not allow illegal MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()
write_clat_ns_p99 195395.92 197942.30 4797.01 1.30%
write_iops 17305.79 17246.56 250.66 -0.34%

write_clat_ns_p99 195543.84 196183.92 5122.88 0.33%
write_iops 17300.61 17310.33 251.56 0.06%

write_clat_ns_p99 195543.84 196990.71 5122.88 0.74%
write_iops 17300.61 17346.32 251.56 0.26%

write_clat_ns_p99 195543.84 196362.24 5122.88 0.42%
write_iops 17300.61 17315.71 251.56 0.09%

It's pure debug stuff and AFAICT is a correct fix...
@Josef, could you test that on your side?

> Ciao, Thorsten
>

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