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    SubjectRe: [RFC v2 8/8] x86, xsave: remove lazy allocation of xstate area
    On Thu, Mar 24, 2011 at 07:39:13AM -0400, Brian Gerst wrote:
    > On Wed, Mar 23, 2011 at 11:27 AM, Hans Rosenfeld <hans.rosenfeld@amd.com> wrote:
    > > This patch completely removes lazy allocation of the xstate area. All
    > > tasks will always have an xstate area preallocated, just like they
    > > already do when non-lazy features are present. The size of the xsave
    > > area ranges from 112 to 960 bytes, depending on the xstates present and
    > > enabled. Since it is common to use SSE etc. for optimization, the actual
    > > overhead is expected to negligible.
    > >
    > > This removes some of the special-case handling of non-lazy xstates. It
    > > also greatly simplifies init_fpu() by removing the allocation code, the
    > > check for presence of the xstate area or init_fpu() return value.
    > >
    > > Signed-off-by: Hans Rosenfeld <hans.rosenfeld@amd.com>
    >
    > I'm not sure I like this. I did a quick test on 64-bit, and found
    > that while most if not all user processes allocated the fpu save area
    > (probably because of glibc blindly initializing the fpu), kernel
    > threads did not. This patch would force kernel threads to allocate
    > memory they would never use.

    Yes, up to a few kilobytes would be wasted by kernel threads. The
    related code gets much simpler. I think that is a good thing.

    Anyway, the patch is not essential for the rework and LWP support, so I
    don't really care that much about it.


    Did you take a look at the other patches? I haven't yet received a
    single comment on them.


    Hans


    --
    %SYSTEM-F-ANARCHISM, The operating system has been overthrown



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