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

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Message-ID: <Z8a-NVJs-pm5W-mG@gmail.com>
Date: Tue, 4 Mar 2025 09:47:49 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, Ard Biesheuvel <ardb@...nel.org>,
	Uros Bizjak <ubizjak@...il.com>,
	Linus Torvalds <torvalds@...uxfoundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 00/11] Add a percpu subsection for cache hot data


* Brian Gerst <brgerst@...il.com> 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.)

Thanks,

	Ingo

View attachment "config" of type "text/plain" (117927 bytes)