linux-kernel - Re: [RFC PATCH 0/2] x86: Fix missing core serialization on migration

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Message-ID: <20171114181732.bwahj6woik27trou@hirez.programming.kicks-ass.net>
Date:   Tue, 14 Nov 2017 19:17:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Avi Kivity <avi@...lladb.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        maged michael <maged.michael@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Dave Watson <davejwatson@...com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrea Parri <parri.andrea@...il.com>,
        "Russell King, ARM Linux" <linux@...linux.org.uk>,
        Greg Hackmann <ghackmann@...gle.com>,
        Will Deacon <will.deacon@....com>,
        David Sehr <sehr@...gle.com>, x86 <x86@...nel.org>
Subject: Re: [RFC PATCH 0/2] x86: Fix missing core serialization on migration

On Tue, Nov 14, 2017 at 07:01:55PM +0100, Daniel Bristot de Oliveira wrote:
> On 11/14/2017 06:40 PM, Peter Zijlstra wrote:
> > On Tue, Nov 14, 2017 at 06:17:13PM +0100, Daniel Bristot de Oliveira wrote:
> > 
> >> IIRC, if the dest cpu is idle and the system is with idle=poll, no IPI
> >> is fired as well, but that is not a very common case.
> > 
> > You're thinking about wake from idle? That is almost always without IPI,
> > even without idle=poll.
> > 
> 
> I meant the resched_curr(rq) of an rq on another CPU. If the dest is
> idle && idle=poll, the IPI will not be send.

I'm saying the IPI will not be send even without idle=poll. MWAIT based
idle will also have TIF_POLLING_NRFLAG set.