Re: [PATCH v4 6/6] arch_topology: Build cacheinfo from primary CPU

[Sudeep Holla <sudeep.holla@arm.com>]

On Tue, Jan 24, 2023 at 02:39:19PM +0000, Conor Dooley wrote:
> On Tue, Jan 24, 2023 at 02:04:20PM +0000, Sudeep Holla wrote:
> > Conor might help me remember the details.
> 
> And I can't shirk either since you know I just replied to Pierre!
> 
> > On Tue, Jan 24, 2023 at 02:50:16PM +0100, Geert Uytterhoeven wrote:
> 
> > > > @@ -840,6 +840,14 @@ void __init init_cpu_topology(void)
> > > >                 reset_cpu_topology();
> > > >                 return;
> > > >         }
> > > > +
> > > > +       for_each_possible_cpu(cpu) {
> > > > +               ret = fetch_cache_info(cpu);
> > > > +               if (ret) {
> > > > +                       pr_err("Early cacheinfo failed, ret = %d\n", ret);
> > > 
> > > This triggers on all my RV64 platforms (K210, Icicle, Starlight,
> > > RZ/Five).
> > > 
> > > This seems to be a respin of
> > > https://lore.kernel.org/all/CAMuHMdUBZ791fxCPkKQ6HCwLE4GJB2S35QC=SQ+X8w5Q4C_70g@mail.gmail.com
> > > which had the same issue.
> > >
> > 
> > I need to recollect my memories reading all the thread, but even after the
> > fixes there were few platforms that failed with so early allocation but were
> > fine with initcalls. Are these such platforms or am I mixing up things here ?
> > Do you still see all the cacheinfo in the sysfs with initcalls that happen
> > later in the boot ?
> 
> IIRC that stuff was failing back then because riscv calls
> init_cpu_topology() far sooner in boot than arm64 does, and therefore
> caused allocation failures. You made that warning go away in the below
> patch by moving detect_cache_attributes() to update_siblings_masks(),
> which both arches call later during boot IIRC:
> https://lore.kernel.org/all/20220713133344.1201247-1-sudeep.holla@arm.com
> 
> Pierre's patch has added fetch_cache_info() to the problematic
> init_cpu_topology() which is called before we can actually do any
> allocation in smp_prepare_boot_cpu() or something like that.
> 
> That's what I get for only reviewing the patch that was specifically for
> riscv, and not the rest of the series... D'oh.
> 
> This actually came up a few weeks ago, although I kinda considered the
> reason it was triggered to be a bit bogus there, since that dmips property
> is not (yet?) a valid property on RISC-V. The patch for that is here:
> https://patchwork.kernel.org/project/linux-riscv/patch/20230105033705.3946130-1-leyfoon.tan@starfivetech.com/
> I tried it on a PolarFire SoC (unfortunately not an Icicle, I just went
> and bricked mine an hour ago) & it should be a fix for this problem too.
> 
> My suggested commit message for that is somewhat prophetic now that I
> look back at it:
> https://lore.kernel.org/all/Y7V4byskevAWKM3G@spud/
>

Ah, that thread, I remember that :).

I still need to understand how this is related to memory allocation.
Pierre was suggesting(in private) if we need to keep fetch_cache_info()
arch specific but I really don't want to go down that patch until I
understand and there is no other option.

Thanks for your time. I will try to recall boot flow and see if I can
gather the reasoning for the seen behaviour.

-- 
Regards,
Sudeep