Re: [External] Re: [PATCH v6 00/11] Parallel CPU bringup for x86_64

[Usama Arif]

On 06/02/2023 08:28, David Woodhouse wrote:
> On Sun, 2023-02-05 at 13:17 -0600, Russ Anderson wrote:
> > Gave the v6 patchset a try on a system with 1920 logocal cpus
> > (sixteen 60 core Sapphire Rapids sockets with Hyperthreadding
> > enabled).
> >
> > Without the patchset it took 71 seconds to start all the cpus.
> > With the v6 patchset it took 14 seconds to start all the cpus,
> > a reduction of 57 seconds.  That is impressive.
> >
> > Full boot, to root login prompt, without patches takes 223 seconds.
> > This patchset reduces the full boot time by 57 seconds, a 25%
> > reduction.
>
> Nice; thanks for testing.
>
> Is that with just the "part1" patch series which has been posted, or
> also with the 'parallel part 2' still taking shape in the tree at
> https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-6.2-rc6
>
> I believe Usama said the second phase of parallelism didn't really help
> much in terms of overall timing? Confirming that *without* all the
> debug prints would be interesting. And we can look for what still
> *could* be made parallel.

I think it would be interesting to get the numbers for such a big 
machine for 3 cases: part1, part1+reuse timer calibration and part1+part2.

Russ mentioned testing v6, so I guess the above numbers are for 
part1+reuse timer calibration.

For my machine the smpboot times were:

No patches: 700ms
part 1:100ms
part1+reuse timer calibration: 30ms
part1+part2: 30ms

Thanks,
Usama