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Date: Fri, 1 May 2015 18:37:09 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Rik van Riel <riel@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, williams@redhat.com,
        Andrew Lutomirski <luto@kernel.org>, fweisbec@redhat.com,
        Peter Zijlstra <peterz@infradead.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable
 & enable from context tracking on syscall entry
Message-ID: <20150501163709.GC1327@gmail.com>
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* Ingo Molnar <mingo@kernel.org> wrote:

> > 2. To suppress the timing tick, we need to get some timing for, 
> > um, the scheduler?  I wasn't really sure about this one.
> 
> So we have variable timeslice timers for the scheduler implemented, 
> they are off by default but they worked last someone tried them. See 
> the 'HRTICK' scheduler feature.
> 
> And for SCHED_FIFO that timeout can be 'never' - i.e. essentially 
> stopping the scheduler tick. (within reason.)

Also note that this bit in context_tracking_enter():

                        if (state == CONTEXT_USER) {
                                trace_user_enter(0);
                                vtime_user_enter(current);
                        }


is related to precise time measurement of user/kernel execution times, 
it's not needed by the scheduler at all, it's just exported to 
tooling. It's not fundamental to the scheduler.

Thanks,

	Ingo