Messages in this thread | | | Date | Wed, 1 Apr 2015 10:29:35 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 7/9] x86/asm/entry/32: tidy up some instructions |
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* Denys Vlasenko <dvlasenk@redhat.com> wrote:
> After TESTs, use logically correct JZ mnemonic instead of JE > (this doesn't change code). > > Tidy up CMPW insns: > > Modern CPUs are not good with 16-bit operations. > The instructions with 16-bit immediates are especially bad, > on many CPUs they cause length changing prefix stall > in the decoders, costing ~6 cycles to recover. > > Replace CMPWs with CMPLs. > Of these, for form with 8-bit sign-extended immediates > it is a win because they are smaller now > (no 0x66 prefix anymore); > ones with 16-bit immediates are faster.
This patch does JE->JZ transitions, but it also does CMPW instruction tweaking - which was buggy as Brian (miraculously!) noticed.
This isn't the first such incident, and I made this point about three times already in the past, but it appears I've not made it loud enough: which part of 'do not put two unrelated changes into the same patch' did you not understand??
We _DO NOT PUT_ multiple, unrelated changes to assembly files into a single patch! And we _especially_ don't mix them up under a meaningless, repetitive, misleading 'tidy up instructions' title!
Full stop.
The titles of the two patches should have been something like:
x86/asm/entry/32: Convert JNE to JNZ mnemonics, to improve readability x86/asm/entry/32: Optimize CMPW to CMPL instructions, to make use of automatic zero-extend
We were lucky that Brian was alert enough to have read through a misleadingly titled, seemingly harmless patch and noticed the bug in your patch, but heck you made it hard!!!
And no, it's not a problem if you create a dozen trivial looking patches and have to wait a bit more for them to trickle into the maintainer tree: asm patches are seldom trivial, and even if they are trivial, both reviewability and bisectability will improve from the process.
You are doing a nice job improving the x86/asm/entry code, but if you cannot create suitably conservative, maximally reviewable and maximally bisectable patches to x86/asm then I won't be able to apply assembly patches from you!
</rant>
Thanks,
Ingo
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