Check context every 128 labels instead of 100 #14118
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Follow up on prometheus#14096 As promised, I bring a benchmark, which shows a very small improvement if context is checked every 128 iterations of label instead of every 100. It's much easier for a computer to check modulo 128 than modulo 100. This is a very small 0-2% improvement but I'd say this is one of the hottest paths of the app so this is still relevant. Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
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@jesusvazquez nerd-sniped me, so I'll do the same with the rest, here's the difference in assembly between doing modulo 128 and modulo 100: TEXT main.modulo128eq0(SB), NOSPLIT|NOFRAME|ABIInternal, $0-8
FUNCDATA $0, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
FUNCDATA $1, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
FUNCDATA $5, main.modulo128eq0.arginfo1(SB)
FUNCDATA $6, main.modulo128eq0.argliveinfo(SB)
PCDATA $3, $1
TESTQ $127, AX
SETEQ AL
RET
TEXT main.modulo100eq0(SB), NOSPLIT|NOFRAME|ABIInternal, $0-8
FUNCDATA $0, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
FUNCDATA $1, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
FUNCDATA $5, main.modulo100eq0.arginfo1(SB)
FUNCDATA $6, main.modulo100eq0.argliveinfo(SB)
PCDATA $3, $1
MOVQ $-8116567392432202711, CX
IMULQ AX, CX
MOVQ $368934881474191032, DX
ADDQ DX, CX
ROLQ $62, CX
MOVQ $184467440737095516, DX
CMPQ DX, CX
SETCC AL
RET |
jesusvazquez
approved these changes
May 21, 2024
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LGTM learned something new today with this
a % 128 = 0 is the same as a & 127 = 0
Which is a faster operation since it just requires doing the AND and not the whole divison and remainer comparison https://godbolt.org/z/4ETM4W8b7
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Small clarifications: there is no need to explicitly rewrite |
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Follow up on #14096
As promised, I bring a benchmark, which shows a very small improvement if context is checked every 128 iterations of label instead of every 100.
It's much easier for a computer to check modulo 128 than modulo 100. This is a very small 0-2% improvement but I'd say this is one of the hottest paths of the app so this is still relevant.