linux-kernel - Re: [PATCH 5/9] x86/mm/tlb: Optimize local TLB flushes

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Message-ID: <09591002-92C0-4D1D-AA4B-FB1C49661A59@vmware.com>
Date:   Wed, 26 Jun 2019 16:39:00 +0000
From:   Nadav Amit <namit@...are.com>
To:     Andy Lutomirski <luto@...nel.org>
CC:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 5/9] x86/mm/tlb: Optimize local TLB flushes

> On Jun 26, 2019, at 9:33 AM, Andy Lutomirski <luto@...nel.org> wrote:
> 
> On Tue, Jun 25, 2019 at 2:36 PM Dave Hansen <dave.hansen@...el.com> wrote:
>> On 6/12/19 11:48 PM, Nadav Amit wrote:
>>> While the updated smp infrastructure is capable of running a function on
>>> a single local core, it is not optimized for this case.
>> 
>> OK, so flush_tlb_multi() is optimized for flushing local+remote at the
>> same time and is also (near?) the most optimal way to flush remote-only.
>> But, it's not as optimized at doing local-only flushes.  But,
>> flush_tlb_on_cpus() *is* optimized for local-only flushes.
> 
> Can we stick the optimization into flush_tlb_multi() in the interest
> of keeping this stuff readable?

flush_tlb_on_cpus() will be much simpler once I remove the fallback
path that is in there for Xen and hyper-v. I can then open-code it in
flush_tlb_mm_range() and arch_tlbbatch_flush().

> 
> Also, would this series be easier to understand if there was a patch
> to just remove the UV optimization before making other changes?

If you just want me to remove it, I can do it. I don’t know who uses it and
what the impact might be.