Messages in this thread | | | Date | Thu, 28 May 2009 13:57:30 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels |
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Nick Piggin wrote: > FWIW, we had to disable paravirt in our default SLES11 kernel. > (admittedly this was before some of the recent improvements were > made).
Yes, I think you'll find it worth trying with it enabled again. The spinlock thing clearly slowed things down, but when that's disabled the difference to native is very small.
> But OTOH, almost any bit feature is going to cost performance. I don't > think this is something new (as noted with CONFIG_SECURITY). It is > just something people have to trade off and decide for themselves. > If you make it configurable and keep performance as good as reasonably > possible, then I don't think more can be asked. >
Yes, that's exactly my point. If I've worked on a feature, I clearly want people to use that feature. Part of making it useful is to make the distro/vendor/user decision to enable that feature as easy as possible, by making the tradeoffs simple.
But tradeoffs are always going to cut both ways: positive (kernel automatically works in a wider range of environments), and negative (performance questions, complexity, etc). Ultimately its the distro's decision to enable a particular feature, and the distro's responsibility to cope with the consequences of that.
> If performance overhead is too much and/or too few users can take > advantage of a feature, then distros can always special-case it. I > think may did for pae...
I think that would be a clear sign of a problem. The whole point of pvops is to avoid needing multiple kernel builds.
J
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