Re: [PATCH 0/9] Parallel CPU bringup for x86_64

[David Woodhouse]

On Wed, 2023-02-01 at 20:43 +0000, Usama Arif wrote:
> This patchseries is from the work done by David Woodhouse (v4: https://lore.kernel.org/all/20220201205328.123066-1-dwmw2@xxxxxxxxxxxxx/).
> The parallel CPU bringup is disabled for all AMD CPUs in this version: (see discussions: https://lore.kernel.org/all/bc3f2b1332c4bb77558df8aa36493a55542fe5b9.camel@xxxxxxxxxxxxx/ and
> https://lore.kernel.org/all/3b6ac86fdc800cac5806433daf14a9095be101e9.camel@xxxxxxxxxxxxx/).
> 
> Doing INIT/SIPI/SIPI in parallel brings down the time for smpboot from ~700ms
> to 100ms (85% improvement) on a server with 128 CPUs split across 2 NUMA
> nodes.
> 
> Adding another cpuhp state for do_wait_cpu_initialized to make sure cpu_init
> is reached in parallel as proposed by David in v1 will bring it down further
> to ~30ms. Making this change would be dependent on this patchseries, so they
> could be explored if this gets merged.
> 
> Changes across versions:
> v2: Cut it back to just INIT/SIPI/SIPI in parallel for now, nothing more
> v3: Clean up x2apic patch, add MTRR optimisation, lock topology update
>     in preparation for more parallelisation.
> v4: Fixes to the real mode parallelisation patch spotted by SeanC, to
>     avoid scribbling on initial_gs in common_cpu_up(), and to allow all
>     24 bits of the physical X2APIC ID to be used. That patch still needs
>     a Signed-off-by from its original author, who once claimed not to
>     remember writing it at all. But now we've fixed it, hopefully he'll
>     admit it now :)
> v5: rebase to v6.1 and remeasure performance, disable parallel bringup
>     for AMD CPUs.

Thanks, Usama.

I've updated to v6.2-rc6 since there were a few more tweaks required
(and we should double-check that the new handling of cache_ap_init from
a dedicated cpuhp step works right if that ends up being done in
parallel).

I also fixed up the complaints from the test robot; including
<linux/smpboot.h> from smpboot.c and making do_cpu_up() static, and
putting #ifdef CONFIG_SMP around the 'are we booting the AP?' check and
code segment in head_64.S.

I've made the AMD thing a CPU bug as Peter suggested, and pushed it to
https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-6.2-rc6
for you to do the real work of actually testing it :)

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