Re: page fault scalability patch V11 [0/7]: overview

Nick Piggin
2004-11-20T03:58:36Z

William Lee Irwin III wrote:
> William Lee Irwin III wrote:
>
>>>Irrelevant. Unshare cachelines with hot mm-global ones, and the
>>>"problem" goes away.
>
>
> On Sat, Nov 20, 2004 at 02:14:33PM +1100, Nick Piggin wrote:
>
>>That's the idea.
>
>
>
> William Lee Irwin III wrote:
>
>>>This stuff is going on and on about some purist "no atomic operations
>>>anywhere" weirdness even though killing the last atomic operation
>>>creates problems and doesn't improve performance.
>
>
> On Sat, Nov 20, 2004 at 02:14:33PM +1100, Nick Piggin wrote:
>
>>Huh? How is not wanting to impact single threaded performance being
>>"purist weirdness"? Practical, I'd call it.
>
>
> Empirically demonstrate the impact on single-threaded performance.
>

I can tell you its worse. I don't have to demonstrate anything, more
atomic RMW ops in the page fault path is going to have an impact.

I'm not saying we must not compromise *anywhere*, but it would
just be nice to try to avoid making the path heavier, that's all.
I'm not being purist when I say I'd first rather explore all other
options before adding atomics.

But nevermind arguing, it appears Linus' suggested method will
be fine and *does* mean we don't have to compromise.

>
> On Sat, Nov 20, 2004 at 01:40:40PM +1100, Nick Piggin wrote:
>
>>>Why the Hell would you bother giving each cpu a separate cacheline?
>>>The odds of bouncing significantly merely amongst the counters are not
>>>particularly high.
>
>
> On Sat, Nov 20, 2004 at 02:14:33PM +1100, Nick Piggin wrote:
>
>>Hmm yeah I guess wouldn't put them all on different cachelines.
>>As you can see though, Christoph ran into a wall at 8 CPUs, so
>>having them densly packed still might not be enough.
>
>
> Please be more specific about the result, and cite the Message-Id.
>

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