* Ingo Molnar <mingo@xxxxxxx> wrote:
> Find below a debug patch i use to run with a configurable spread.
>
> Note, i just ran the patch on a different system and there the effect was
> much less pronounced. So i'd prefer independent confirmation as well that it
> speeds up things for others as well.
>
> I'll run more numbers - maybe we are just very sensitive to the exact layout
> of the object hash and a 16x spread created a different, more optimal layout.
Here are those numbers:
$ for ((size=2; size<24; size++)); do printf "%5d: " $size; perf stat -e instructions:u -e cycles:u -e task-clock --sync --repeat 10 ./git --object-hash-spread $size gc 2>&1 | grep cycles; done
2: 9,362,801,669 cycles:u # 2.982 GHz ( +- 0.25% )
3: 9,464,946,158 cycles:u # 2.993 GHz ( +- 1.17% )
4: 9,382,214,358 cycles:u # 2.981 GHz ( +- 0.26% )
5: 9,373,537,954 cycles:u # 2.986 GHz ( +- 0.24% )
6: 9,492,635,404 cycles:u # 2.988 GHz ( +- 1.25% )
7: 9,427,037,835 cycles:u # 2.982 GHz ( +- 0.19% )
8: 9,311,764,604 cycles:u # 2.987 GHz ( +- 0.23% )
9: 9,384,331,920 cycles:u # 2.985 GHz ( +- 0.27% )
10: 9,388,460,044 cycles:u # 2.983 GHz ( +- 0.31% )
11: 9,374,380,165 cycles:u # 2.984 GHz ( +- 0.25% )
12: 9,417,466,827 cycles:u # 2.984 GHz ( +- 0.27% )
13: 9,348,550,619 cycles:u # 2.982 GHz ( +- 0.12% )
14: 9,369,435,508 cycles:u # 2.982 GHz ( +- 0.31% )
15: 9,361,127,598 cycles:u # 2.983 GHz ( +- 0.27% )
16: 9,402,077,866 cycles:u # 2.987 GHz ( +- 0.20% )
17: 9,390,950,850 cycles:u # 2.985 GHz ( +- 0.27% )
18: 9,355,126,542 cycles:u # 2.986 GHz ( +- 0.30% )
19: 9,357,143,371 cycles:u # 2.974 GHz ( +- 0.33% )
20: 9,372,977,607 cycles:u # 2.985 GHz ( +- 0.34% )
21: 9,355,406,722 cycles:u # 2.985 GHz ( +- 0.45% )
22: 9,342,730,882 cycles:u # 2.982 GHz ( +- 0.31% )
23: 9,372,321,792 cycles:u # 2.982 GHz ( +- 0.28% )
They are utterly unconvincing - there seems to be no improvement, it's all
within noise.
Thanks,
Ingo
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