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Date: Fri, 9 Sep 2016 09:44:56 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Benjamin Serebrin <serebrin@google.com>,
        Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>,
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        Andrew Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>,
        Mel Gorman <mgorman@suse.de>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH RFC v6] x86,mm,sched: make lazy TLB mode even lazier
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On Thu, Sep 08, 2016 at 09:39:45PM -0700, Andy Lutomirski wrote:
> If they're busy threads, shouldn't the yield return immediately
> because the threads are still ready to run?  Lazy TLB won't do much
> unless you get the kernel in some state where it's running in the
> context of a different kernel thread and hasn't switched to
> swapper_pg_dir.  IIRC idle works like that, but you'd need to actually
> sleep to go idle.

Right, a task doing:

	for (;;) sched_yield();

esp. when its the only runnable thread on the CPU, is a busy thread. It
will not enter switch_mm(), which was where the invalidate hook was
placed IIRC.