Re: [PATCH] Parallel microcode update in Linux

[Pavel Machek <pavel@ucw.cz>]

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

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