Re: [PATCH] x86/asm/entry/64: pack interrupt dispatch table tighter

From: H. Peter Anvin
Date: Fri Apr 03 2015 - 14:36:22 EST

On 04/03/2015 11:08 AM, Linus Torvalds wrote:
> On Fri, Apr 3, 2015 at 9:54 AM, Denys Vlasenko <dvlasenk@xxxxxxxxxx> wrote:
>> How about this version?
>> It's still isn't a star of readability,
>> but the structure of the 32-byte code block is more visible now...
> Do we really even want to be this clever in the first place?
> The thing is, when we take an interrupt:
> (a) the L1 I$ is always cold
> (b) the instruction decoder has never had time to run ahead
> (c) there are usually not that many different interrupts anyway, even
> under load (ie you'd have maybe disk and networking)
> (d) we intentionally spread out the different interrupt vector numbers
> (e) the 32-byte block thing is questionable, most older
> micro-architectures fetch in 16-byte blocks iirc.

For the record, I actually measured the impact of the jump-to-jump when
I wrote it. It has a small, *but measurable*, positive impact.


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