Re: [PATCH 2/2] KVM: PPC: Book3S: Call into C interrupt handlers

[Alexander Graf <agraf@xxxxxxx>]

On 27.04.2012, at 18:37, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote:

> On 04/27/2012 06:23 AM, Alexander Graf wrote:
>> 
>> On 27.04.2012, at 07:48, Paul Mackerras wrote:
>> 
>>> Have you measured a performance improvement with this patch?  If so
>>> how big was it?
>> 
>> Yeah, I tried things on 970 in an mfsprg/mtsprg busy loop. I measured 3 different variants:
>> 
>> C irq handling:        1004944 exits/sec
>> asm irq handling:        1001774 exits/sec
>> asm + hsrr patch:        994719 exits/sec
>> 
>> So as you can see, that code change does have quite an impact. But
>> maybe the added complexity isn't worth it? Either way, we should try
>> and find a solution that works the same way for booke and book3s - I
>> don't want such an integral part to differ all that much.
> 
> Is it really added complexity, considering what you can remove from the
> asm?  I went with C handling on bookehv because it seemed simpler (the
> original internal version had asm handling).

Well, the addition in complexity is that you have to start thinking about more things than before :). I'm not sure really which way is better in the long run.


Alex

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