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SubjectRe: [PATCH] Parallel microcode update in Linux
Hi!

> + u64 p0, p1;
> int ret;
>
> atomic_set(&late_cpus_in, 0);
> atomic_set(&late_cpus_out, 0);
>
> + p0 = rdtsc_ordered();
> +
> ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask);
> +
> + p1 = rdtsc_ordered();
> +
> if (ret > 0)
> microcode_check();
>
> pr_info("Reload completed, microcode revision: 0x%x\n", boot_cpu_data.microcode);
>
> + pr_info("p0: %lld, p1: %lld, diff: %lld\n", p0, p1, p1 - p0);
> +
> return ret;
> }
>
> We have used a machine with a broken microcode in BIOS and no microcode in
> initramfs (to bypass early loading).
>
> Here are the results for parallel loading (we made two measurements):

> [ 18.197760] microcode: updated to revision 0x200005e, date = 2019-04-02
> [ 18.201225] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
> [ 18.201230] microcode: Reload completed, microcode revision: 0x200005e
> [ 18.201232] microcode: p0: 118138123843052, p1: 118138153732656, diff: 29889604

> Here are the results of serial loading:
>
> [ 17.542518] microcode: updated to revision 0x200005e, date = 2019-04-02
> [ 17.898365] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
> [ 17.898370] microcode: Reload completed, microcode revision: 0x200005e
> [ 17.898372] microcode: p0: 149220216047388, p1: 149221058945422, diff: 842898034
>
> One can see that the difference is an order magnitude.

Well, that's impressive, but it seems to finish 300 msec later? Where does that difference
come from / how much real time do you gain by this?

Best regards,
Pavel

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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