linux-kernel - Re: [PATCH 0/2] x86/context-tracking: Remove last remaining calls to exception_enter/exception

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Date:   Mon, 6 Jan 2020 16:05:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 0/2] x86/context-tracking: Remove last remaining calls to
 exception_enter/exception_exit()

On Fri, Dec 27, 2019 at 05:36:10PM +0100, Frederic Weisbecker wrote:
> Thanks to the cleanups from Andy Lutomirski over the years, those calls
> can now be removed. This will allow for nice things in the future for
> x86 support on full nohz:
> 
> * Remove TIF_NOHZ and use a per-cpu switch to enable, disable context
>   tracking.
> 
> * Avoid context tracking on housekeepers.
> 
> * Dynamically enable/disable context tracking on CPU on runtime and
>   therefore allow runtime enable/disable of nohz_full
> 
> * Make nohz_full a property of cpuset.
> 
> Frederic Weisbecker (2):
>   x86/context-tracking: Remove exception_enter/exit() from
>     do_page_fault()
>   x86/context-tracking: Remove exception_enter/exit() from
>     KVM_PV_REASON_PAGE_NOT_PRESENT async page fault

Thanks, these look good to me.

Did I tell you about my 'TODO' item vs text_poke_sync() ? Basically, we
can avoid sending the IPI to NOHZ_FULL user CPUs, provided we make their
enter_from_user_mode() do the sync_core().