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SubjectRe: [ckrm-tech] [RFC 0/4] sched: Add CPU rate caps (improved)
Peter Williams wrote:

> 4. Overhead Measurements. To measure the implications for overhead
> introduced by these patches kernbench was used on a dual 500Mhz
> Centrino SMP system. Runs were done for a kernel without these
> patches applied, one with the patches applied but no caps being used
> and one with the patches applied and running kernbench with a soft cap
> of zero (which would be inherited by all its children).
>
> Average Optimal -j 8 Load Run:
>
> Vanilla Patch Applied Soft Cap 0%
>
> Elapsed Time 1056.1 (1.92) 1048.2 (0.62) 1064.1 (1.59)
> User Time 1908.1 (1.09) 1895.2 (1.30) 1926.6 (1.39)
> System Time 181.7 (0.60) 177.5 (0.74) 173.8 (1.07)
> Percent CPU 197.6 (0.55) 197.0 (0) 197.0 (0)
> Context Switches 49253.6 (136.31) 48881.4 (92.03) 92490.8 (163.71)
> Sleeps 28038.8 (228.11) 28136.0 (250.65) 25769.4 (280.40)

I tried to run kernbench with hard cap, and then it spent a very
long time on "Cleaning souce tree..." phase. Because this phase
is not CPU hog, my expectation is that it act as without cap.

That can be reproduced by just running "make clean" on top of a
kernel source tree with hard cap.

% /usr/bin/time make clean
1.62user 0.29system 0:01.90elapsed 101%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+68539minor)pagefaults 0swaps

# Without cap, it returns almost immediately

% ~/withcap.sh -C 900 /usr/bin/time make clean
1.61user 0.29system 1:26.17elapsed 2%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+68537minor)pagefaults 0swaps

# With 90% hard cap, it takes about 1.5 minutes.

% ~/withcap.sh -C 100 /usr/bin/time make clean
1.64user 0.34system 3:31.48elapsed 0%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+68538minor)pagefaults 0swaps

# It became worse with 10% hard cap.

% ~/withcap.sh -c 900 /usr/bin/time make clean
1.63user 0.28system 0:01.89elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+68537minor)pagefaults 0swaps

# It doesn't happen with soft cap.

Thanks,
MAEDA Naoaki

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