Re: [PATCH v3 00/11] Add a percpu subsection for cache hot data

[Brian Gerst]

On Tue, Mar 4, 2025 at 3:47 AM Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
>
> * Brian Gerst <brgerst@xxxxxxxxx> wrote:
>
> > >
> > > -       PERCPU_SECTION(INTERNODE_CACHE_BYTES)
> > > +       PERCPU_SECTION(L1_CACHE_BYTES)
> > >         ASSERT(__per_cpu_hot_end - __per_cpu_hot_start <= 64, "percpu cache hot section too large")
> > >
> > >         RUNTIME_CONST_VARIABLES
> > >
> >
> > That is probably the right call.  The initial percpu section is just
> > used by the boot cpu early and as a template for the dynamically
> > allocated percpu memory, which should account for the proper
> > alignment for NUMA.
>
> Okay.
>
> Randconfig testing found another corner case with the attached config:
>
>     KSYMS   .tmp_vmlinux0.kallsyms.S
>     AS      .tmp_vmlinux0.kallsyms.o
>     LD      .tmp_vmlinux1
>   ld: percpu cache hot section too large
>   make[2]: *** [scripts/Makefile.vmlinux:77: vmlinux] Error 1
>
> (I haven't figured out the root cause yet.)

CONFIG_MPENTIUM4 sets X86_L1_CACHE_SHIFT to 7 (128 bytes).


Brian Gerst