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SubjectRe: [patch] lazy I/O bitmap copy for i386 (ver 2) ...
On Tue, 24 Aug 2004, Davide Libenzi wrote:

> The following patch implements the lazy I/O bitmap copy for the i386
> architecture. It uses an invalid bitmap offset inside the TSS to eventually
> handle the correct bitmap update in the GPF handler. The logic is the same
> of the first version, plus the usage of get/put_cpu() (thx Brian) and the
> nesting over the latest Ingo variable bitmap bits.

As followup, I instrumented the switchto code to do something like:

if (prev->io_bitmap_ptr) {
if (tss->io_bitmap_base == INVALID_IO_BITMAP_OFFSET_LAZY)
no_hit_gpf++;
else
hit_gpf++;
}

After a couple of minutes of light X usage I get:

Hit: 1017
NoHit: 29541

This is FC1 up-to-date (yesterday's ~60% rate was due an incorrect test
performed in the instrumentation code). Did not run any perf test, but for
sure updating an unsigned long should result faster than memcpy/memset
memory regions, during context switches.



- Davide

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