linux-kernel - Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry

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


* Ingo Molnar <mingo@...nel.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
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