Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels | Date | Fri, 5 Jun 2009 14:16:18 +0930 |
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On Fri, 5 Jun 2009 12:32:14 am Linus Torvalds wrote: > So I think your minimum and maximum configs should at least _match_ in > HIGHMEM. Limiting memory to not actually having any (with "mem=880M") will > avoid the TLB flushing impact of HIGHMEM, which is clearly going to be the > _bulk_ of the overhead, but HIGHMEM is still going to be noticeable on at > least some microbenchmarks.
Well, Ingo was ranting because (paraphrase) "no other config option when *unused* has as much impact as CONFIG_PARAVIRT!!!!!!!!!!".
That was the point of my mail; facts show it's simply untrue.
> The comparison is ugly and pointless. (Re: SMP)
Distributions don't ship UP kernels any more; this shows what that costs if you're actually on a UP box. If we really don't care, perhaps we should make CONFIG_SMP=n an option under EMBEDDED for x86. And we can rip out the complex patching SMP patching stuff too.
> Something like CONFIG_HIGHMEM* or CONFIG_SMP is not really what I'd ever > call "optional feature", although I hope to Dog that CONFIG_HIGHMEM can > some day be considered that some day.
Someone from a distro might know how many deployed machines don't need them. Kernel hackers tend to have modern machines; same with "enterprise" sites. I have no idea.
Without those facts, I'll leave further discussion to someone else :)
Thanks, Rusty.
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