Re: [RFC v2 8/8] x86, xsave: remove lazy allocation of xstate area

[Hans Rosenfeld <hans.rosenfeld@amd.com>]

On Tue, Mar 29, 2011 at 11:27:50AM -0400, H. Peter Anvin wrote:
> On 03/29/2011 07:17 AM, Hans Rosenfeld wrote:
> >>
> >> 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.
> > 
> 
> This is silly.  It shouldn't be very hard to allocate this for user
> threads while avoiding the allocation for kernel threads.  The only
> excuse for allocating it for user threads is if it becomes part of the
> kernel stack allocation.

The allocation itself is not what I'm concerned about. I'm more worried
about the code that always has to check whether a thread has a xstate
area allocated or not. But I will try and find out to get this done the
way you suggested.


Meanwhile, could you please review the other patches? They are much more
important to me.


Hans


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