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SubjectRe: [PATCH] x86: Intel microcode loader performance improvement
Dmitry Adamushko wrote:
> On 5 March 2010 18:42, Dimitri Sivanich <sivanich@sgi.com> wrote:
>> We've noticed that on large SGI UV system configurations, running
>> microcode.ctl can take very long periods of time. This is due to
>> the large number of vmalloc/vfree calls made by the Intel
>> generic_load_microcode() logic.
>>
>> By reusing allocated space, the following patch reduces the time
>> to run microcode.ctl on a 1024 cpu system from approximately 80
>> seconds down to 1 or 2 seconds.
>>
>> Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
>
> This approach seems reasonable in the scope of the current framework.
>
> Acked-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
>
> However, I think a better approach would be to have some kind of
> shared storage for loaded microcode updates. Given that for the
> majority of SMP systems all the cpus are normally updated to the very
> same new instance of microcode, it should be enough to do a search for
> the first cpu, cache the instance of microcode and then reuse it for
> others.
>
The assumption that all CPUs are the same is not always true in practice, people
buy a system and don't always fully populate initially, and when they add
processors, they have a more recent stepping. So reusing microcode or updating
in parallel would add complexity, and 2 sec for 1024 CPUs puts a pretty low
upper bound on possible improvement. Does more improvement to a one time small
delay justify additional complexity?

Systems that size are probably not booted all that often. Something to consider
before putting a lot of effort into it, I think.

--
Bill Davidsen <davidsen@tmr.com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot


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