On Sunday 05 November 2006 17:12, Linus Torvalds wrote:
> And changing restore-flags to a "conditional branch around sti"
Yes of course.
> is likely
> not much better
We'll see.
It used to be a bad idea because everything was inline, but these
days with out of line code one can be much more flexible.
> - mispredicted branches on a P4 are potentially worse than
> the popf cost.
They are far less than 48 cycles. The P4 is not _that_ bad in this
area.
> Side note: for the netburst microarchitecture - aka P4 - in general,
> something like 48 cycles is a _good_ thing. I measured a internal
> micro-fault for marking a page table entry dirty at over 1500 cycles!
> There's a reason Intel dropped Netburst in favour of Core 2 - which is
> largely just an improved Pentium Pro uarch. Admittedly, the "just" is a
> bit unfair, because there's a _lot_ of improvement, but still..
>
> So you should never actually make any real code design decisions based on
> a P4 result. The P4 is goign away, and it was odd.
There are millions and millions of P4s out there running
Linux and I don't think that will change any time soon (in fact Intel will
be still shipping many new ones for a long time) If there are cheap
valuable optimizations for P4 that don't impact others much I'm all for them.
-Andi
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