linux-kernel - Re: [PATCH v3 5/9] x86/mm/tlb: Privatize cpu

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Date:   Fri, 19 Jul 2019 18:54:00 +0000
From:   Nadav Amit <namit@...are.com>
To:     Dave Hansen <dave.hansen@...el.com>
CC:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3 5/9] x86/mm/tlb: Privatize cpu_tlbstate

> On Jul 19, 2019, at 11:48 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> 
> On 7/19/19 11:43 AM, Nadav Amit wrote:
>> Andy said that for the lazy tlb optimizations there might soon be more
>> shared state. If you prefer, I can move is_lazy outside of tlb_state, and
>> not set it in any alternative struct.
> 
> I just wanted to make sure that we capture these rules:
> 
> 1. If the data is only ever accessed on the "owning" CPU via
>   this_cpu_*(), put it in 'tlb_state'.
> 2. If the data is read by other CPUs, put it in 'tlb_state_shared'.
> 
> I actually like the idea of having two structs.

Yes, that’s exactly the idea. In the (1) case, we may even be able to mark
the struct with __thread qualifier, which IIRC would prevent memory barriers
from causing these values being reread.