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

[H. Peter Anvin]

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.

	-hpa

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