Re: [PATCH v4 0/6] LoongArch: Add pv ipi support on LoongArch VM
From: WANG Xuerui
Date: Thu Feb 22 2024 - 05:14:20 EST
On 2/22/24 18:06, maobibo wrote:
On 2024/2/22 下午5:34, WANG Xuerui wrote:
On 2/17/24 11:15, maobibo wrote:
On 2024/2/15 下午6:25, WANG Xuerui wrote:
On 2/15/24 18:11, WANG Xuerui wrote:
Sorry for the late reply (and Happy Chinese New Year), and thanks
for providing microbenchmark numbers! But it seems the more
comprehensive CoreMark results were omitted (that's also absent in
v3)? While the
Of course the benchmark suite should be UnixBench instead of
CoreMark. Lesson: don't multi-task code reviews, especially not
after consuming beer -- a cup of coffee won't fully cancel the
influence. ;-)
Where is rule about benchmark choices like UnixBench/Coremark for ipi
improvement?
Sorry for the late reply. The rules are mostly unwritten, but in
general you can think of the preference of benchmark suites as a
matter of "effectiveness" -- the closer it's to some real workload in
the wild, the better. Micro-benchmarks is okay for illustrating the
points, but without demonstrating the impact on realistic workloads, a
change could be "useless" in practice or even decrease various
performance metrics (be that throughput or latency or anything that
matters in the certain case), but get accepted without notice.
yes, micro-benchmark cannot represent the real world, however it does
not mean that UnixBench/Coremark should be run. You need to point out
what is the negative effective from code, or what is the possible real
scenario which may benefit. And points out the reasonable benchmark
sensitive for IPIs rather than blindly saying UnixBench/Coremark.
I was not meaning to argue with you, nor was I implying that your
changes "must be regressing things even though I didn't check myself" --
my point is, *any* comparison with realistic workload that shows the
performance mostly unaffected inside/outside KVM, would give reviewers
(and yourself too) much more confidence in accepting the change.
For me, personally I think a microbenchmark could be enough, because the
only externally-visible change is the IPI mechanism overhead, but please
consider other reviewers that may or may not be familiar enough with
LoongArch to be able to notice the "triviality". Also, given the 6-patch
size of the series, it could hardly be considered "trivial".
--
WANG "xen0n" Xuerui
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