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Re: FOR REVIEW: New x86-64 vsyscall vgetcpu()
- From: Andi Kleen <ak at suse dot de>
- To: Brent Casavant <bcasavan at sgi dot com>
- Cc: Zoltan Menyhart <Zoltan dot Menyhart at bull dot net>, Jes Sorensen <jes at sgi dot com>, Tony Luck <tony dot luck at intel dot com>, discuss at x86-64 dot org, linux-kernel at vger dot kernel dot org, libc-alpha at sourceware dot org, vojtech at suse dot cz, linux-ia64 at vger dot kernel dot org
- Date: Fri, 16 Jun 2006 17:40:18 +0200
- Subject: Re: FOR REVIEW: New x86-64 vsyscall vgetcpu()
- References: <200606140942.31150.ak@suse.de> <200606161656.40930.ak@suse.de> <20060616102516.A91827@pkunk.americas.sgi.com>
> To this last point, it might be more reasonable to map in a page that
> contained a new structure with a stable ABI, which mirrored some of
> the task_struct information, and likely other useful information as
> needs are identified in the future. In any case, it would be hard
> to beat a single memory read for performance.
That would mean making the context switch and possibly other
things slower.
In general you would need to make a very good case first that all this
complexity is worth it.
> Cache-coloring and kernel bookkeeping effects could be minimized if this
> was provided as an mmaped page from a device driver, used only by
> applications which care.
I don't see what difference that would make. You would still
have the fixed offset problem and doing things on demand often tends
to be even more complex.
-Andi (who thinks these proposals all sound very messy)