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Re: [patch v3 08/36] x86/smpboot: Split up native_cpu_up() into separate phases and document them
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- Date: Tue, 09 May 2023 22:11:05 +0200
- Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, David Woodhouse <dwmw2@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, Arjan van de Veen <arjan@xxxxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Paul McKenney <paulmck@xxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>, Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>, Paul Menzel <pmenzel@xxxxxxxxxxxxx>, "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>, Piotr Gorski <lucjan.lucjanov@xxxxxxxxx>, Usama Arif <usama.arif@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Russell King <linux@xxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Guo Ren <guoren@xxxxxxxxxx>, linux-csky@xxxxxxxxxxxxxxx, Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>, linux-mips@xxxxxxxxxxxxxxx, "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>, Helge Deller <deller@xxxxxx>, linux-parisc@xxxxxxxxxxxxxxx, Paul Walmsley <paul.walmsley@xxxxxxxxxx>, Palmer Dabbelt <palmer@xxxxxxxxxxx>, linux-riscv@xxxxxxxxxxxxxxxxxxx, Mark Rutland <mark.rutland@xxxxxxx>, Sabin Rapan <sabrapan@xxxxxxxxxx>, "Michael Kelley (LINUX)" <mikelley@xxxxxxxxxxxxx>, David Woodhouse <dwmw@xxxxxxxxxxxx>
- Delivery-date: Tue, 09 May 2023 20:11:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, May 09 2023 at 12:04, Peter Zijlstra wrote:
> On Mon, May 08, 2023 at 09:43:39PM +0200, Thomas Gleixner wrote:
> Not to the detriment of this patch, but this barrier() and it's comment
> seem weird vs smp_callin(). That function ends with an atomic bitop (it
> has to, at the very least it must not be weaker than store-release) but
> also has an explicit wmb() to order setup vs CPU_STARTING.
>
> (arguably that should be a full fence *AND* get a comment)
TBH: I'm grasping for something 'arguable': What's the point of this
wmb() or even a mb()?
Most of the [w]mb()'s in smpboot.c except those in mwait_play_dead()
have a very distinct voodoo programming smell.
Thanks,
tglx
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