* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, Jul 8, 2016 at 1:46 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> >
> > Could you please try to find some syscall workload that does many small user
> > copies and thus excercises this code path aggressively?
>
> Any stat()-heavy path will hit cp_new_stat() very heavily. Think the
> usual kind of "traverse the whole tree looking for something". "git
> diff" will do it, just checking that everything is up-to-date.
>
> That said, other things tend to dominate.
So I think a cached 'find /usr >/dev/null' might be a good one as well:
triton:~/tip> strace -c find /usr >/dev/null
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
47.09 0.006518 0 254697 newfstatat
26.20 0.003627 0 254795 getdents
14.45 0.002000 0 1147411 fcntl
7.33 0.001014 0 509811 close
3.28 0.000454 0 128220 1 openat
1.52 0.000210 0 128230 fstat
0.27 0.000016 0 12810 write
0.00 0.000000 0 10 read
triton:~/tip> perf stat --repeat 3 -e cycles:u,cycles:k,cycles find /usr >/dev/null
Performance counter stats for 'find /usr' (3 runs):
1,594,437,143 cycles:u ( +- 2.76% )
2,570,544,009 cycles:k ( +- 2.50% )
4,164,981,152 cycles ( +- 2.59% )
0.929883686 seconds time elapsed ( +- 2.57% )
... and it's dominated by kernel overhead, with a fair amount of memcpy overhead
as well:
1.22% find [kernel.kallsyms] [k] copy_user_enhanced_fast_string
But maybe there are simple shell commands that are even more user-memcpy intense?
Thanks,
Ingo
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