lkml.org 
[lkml]   [2009]   [May]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [benchmark] 1% performance overhead of paravirt_ops on native kernels
    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


    \
     
     \ /
      Last update: 2009-05-28 23:01    [W:3.220 / U:0.044 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site