Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64

[Tom Lendacky]

On 12/16/21 1:52 PM, David Woodhouse wrote:
> On Thu, 2021-12-16 at 10:27 -0600, Tom Lendacky wrote:
> > On 12/15/21 8:56 AM, David Woodhouse wrote:
> >
> > > Doing the INIT/SIPI/SIPI in parallel for all APs and *then* waiting for
> > > them shaves about 80% off the AP bringup time on a 96-thread socket
> > > Skylake box (EC2 c5.metal) — from about 500ms to 100ms.
> > >
> > > There are more wins to be had with further parallelisation, but this is
> > > the simple part.
> >
> > I applied this series and began booting a regular non-SEV guest and hit a
> > failure at 39 vCPUs. No panic or warning, just a reset and OVMF was
> > executing again. I'll try to debug what's going, but not sure how quickly
> > I'll arrive at anything.
>
> I've pushed the SEV-ES fix to
> https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-5.16
> and in doing so I've moved the 'no_parallel_bringup' command line
> argument earlier in the series, to Thomas's "Support parallel startup
> of secondary CPUs" commit (now 191f0899757). It would be interesting to
> see if you can reproduce with just that much, both with and with
> no_parallel_bringup. And then whether the subsequent commit that
> actually enables the parallel INIT/SIPI/SIPI actually makes the
> difference?

I'll pull it down and give it try.

Thanks,
Tom

> Thanks!