Re: [PATCH 0/6] Per-processor private data areas for i386
From: Jeremy Fitzhardinge
Date: Wed Sep 27 2006 - 16:28:40 EST
Pavel Machek wrote:
So we have 4% slowdown...
Yes, that would be the worst-case slowdown in the hot-cache case.
Rearranging the layout of the GDT would remove any theoretical
cold-cache slowdown (I haven't measured if there's any impact in practice).
...and 0.2% smaller kernel. I guess you should demonstrate speedup at
complex syscalls before wedecide it is worth it...
That would be nice, but this patch series isn't really intended to be a
performance improvement. That would be nice, but the main motivation is
to make inline assembler patching for the paravirt work cleaner.
Rusty and I have also been investigating how to use the %gs-based memory
to implement all percpu data, rather than the few special cases this
patch series currently covers, which will help further amortize the
Rusty has also done more comprehensive benchmarks with his variant of
this patch series, and found no statistically interesting performance
difference. Which is pretty much what I would expect, since it doesn't
increase cache-misses at all.
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