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

[Usama Arif]

On 02/02/2023 10:02, David Woodhouse wrote:
> 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 :)

Thanks David! I have tested and reposted the v6.2-rc6 patches. One thing 
I was mistaken about since I had rebased the patches together was that 
the last 100ms to 30ms optimization was coming from parallelization in 
x86/cpu:wait-init, when it seems to have a negligible affect. The last 
70ms optimization was coming mainly from reusing timer calibration. Its 
a simple patch and I have added it at the end of the series. The only 
thing thats' missing was a sign-off from the author who I have added to 
the latest series.