linux-kernel - Re: [PATCH v2] perf trace: Speed up startup time by bypassing the creation of kernel maps

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Message-ID: <CAH0uvohef=2-hE7BBbgNU+OkcY64pZaLgEHJfOq-o+_VsreY3g@mail.gmail.com>
Date: Wed, 30 Apr 2025 16:33:00 -0700
From: Howard Chu <howardchu95@...il.com>
To: Aditya Bodkhe <adityab1@...ux.ibm.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org, 
	namhyung@...nel.org, mark.rutland@....com, alexander.shishkin@...ux.intel.com, 
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com, 
	kan.liang@...ux.intel.com, james.clark@...aro.org, charlie@...osinc.com, 
	mpetlan@...hat.com, vmolnaro@...hat.com, linux@...blig.org, 
	mhiramat@...nel.org, leo.yan@....com, dima@...retsauce.net, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	krzysztof.m.lopatowski@...il.com
Subject: Re: [PATCH v2] perf trace: Speed up startup time by bypassing the
 creation of kernel maps

Hi Aditya,

Sorry for the late reply — I was really sick over the past two weeks.
Anyway, thank you so much for testing this patch on powerpc. Could you
share the commands you used for testing? I noticed a 2-second runtime,
which makes me think you might have used the time sudo ./perf trace --
sleep 1 command I mentioned earlier. However, that command may not be
ideal for benchmarking this patch, as the extra 1-second time makes
performance gain imperceptible.

Personally, I prefer using 'time sudo ./perf trace -C 0 -- true',
tested both with and without the patch. That said, I think it’s also
valid to apply the patch, and test using the following two commands:

# this will not load the kernel map, should be faster.
time sudo ./perf trace -C 0 -- true

# this enables the kernel map, should take longer than the former command
time sudo ./perf trace --call-graph fp --kernel-syscall-graph -C 0 -- true

And these are the results I gathered, all obtained with the patch applied.
perf $ time sudo ./perf trace -C 0 -- true

real    0m0.264s
user    0m0.004s
sys     0m0.009s
perf $ time sudo ./perf trace --call-graph fp --kernel-syscall-graph
-C 0 -- true

real    0m0.462s
user    0m0.004s
sys     0m0.013s

By the way, the 1-second difference in start up time shown in the
commit message, is obtained using an older Lenovo T480, with Intel
i5-8350 processor. The result I gathered above was from a machine with
i7-12700 processor, where the difference is 200ms. And in your
results, the difference is even smaller, which may indicate that your
machine has a better single-core performance, or faster memory, or
other contributing factors.

Would you like a 'Tested-by:' ? :)

Thanks,
Howard