linux-kernel - Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file

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Date:   Sun, 30 Jun 2019 12:29:46 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Julien Grall <julien.grall@....com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        aou@...s.berkeley.edu, gary@...yguo.net,
        Atish Patra <Atish.Patra@....com>, hch@...radead.org,
        paul.walmsley@...ive.com, rppt@...ux.ibm.com,
        linux-riscv@...ts.infradead.org, Anup Patel <anup.Patel@....com>,
        Palmer Dabbelt <palmer@...ive.com>, suzuki.poulose@....com,
        Marc Zyngier <marc.zyngier@....com>, julien.thierry@....com,
        Will Deacon <will.deacon@....com>, christoffer.dall@....com,
        james.morse@....com
Subject: Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a
 separate file

Hi Marinas,

Thx for the reply

On Mon, Jun 24, 2019 at 11:38 PM Catalin Marinas
<catalin.marinas@....com> wrote:
>
> On Mon, Jun 24, 2019 at 12:35:35AM +0800, Guo Ren wrote:
> > On Fri, Jun 21, 2019 at 10:16 PM Catalin Marinas
> > <catalin.marinas@....com> wrote:
> > > BTW, if you find the algorithm fairly straightforward ;), see this
> > > bug-fix which took a formal model to identify: a8ffaaa060b8 ("arm64:
> > > asid: Do not replace active_asids if already 0").
> [...]
> > Btw, Is this detected by arm's aisd allocator TLA+ model ? Or a real
> > bug report ?
>
> This specific bug was found by the TLA+ model checker (at the time we
> were actually tracking down another bug with multi-threaded CPU sharing
> the TLB, bug also confirmed by the formal model).
Could you tell me the ref-link about "another bug with multi-threaded
CPU sharing the TLB" ?

In my concept, the multi-core asid mechanism is also applicable to
multi-thread shared TLB, but it will generate redundant tlbflush. From
the software design logic, multi-threaded is treated as multi-cores
without error, but performance is not optimized. So in my RFC PATCH:
[1], I try to reduce multi-threads' tlbflush in one CPU core with the
fixed cpu ID bitmap hypothesis.

1: https://lore.kernel.org/linux-csky/CAJF2gTQ0xQtQY1t-g9FgWaxfDXppMkFooCQzTFy7+ouwUfyA6w@mail.gmail.com/T/#m2ed464d2dfb45ac6f5547fb3936adf2da456cb65
--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/