linux-kernel - Re: [ANNOUNCE] 4.1.5-rt5 meant to reply to 4.4.1-rt5

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Date:	Fri, 12 Feb 2016 15:36:16 +0100
From:	Tim Sander <tim@...eglstein.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
	John Kacur <jkacur@...hat.com>
Subject: Re: [ANNOUNCE] 4.1.5-rt5 meant to reply to 4.4.1-rt5

Hi Sebastian

As you got correctly i was talking about 4.4.1-rt5 and not 4.1 i replied to by 
accident.

Am Freitag, 12. Februar 2016, 10:07:59 schrieb Sebastian Andrzej Siewior:
> On 02/12/2016 09:28 AM, Tim Sander wrote:
> > Hi Sebastian
> 
> Hi Tim,
> 
> > Am Sonntag, 16. August 2015, 15:56:30 schrieb Sebastian Andrzej Siewior:
> >> I'm pleased to announce the v4.1.5-rt5 patch set.
> > 
> > I have just tested it with a Altera SoC ARM v7. The latencies seem to have
> > gotten a little bit worse with each release. The first core has always
> > been
> > worse (presumably due to interrupt load) but now it dropped to 111µs (rt5)
> > from 76µs(rt3) and 54µs(rt2).
> 
> in -rt2 we had bug in migrate disable code which means each task was
> running on CPU0. This got partly fixed in -rt3. In -rt3 the scheduler
> could assign a task to CPU1 but the task should stay there for ever.
> This little detail was fixed in -rt5.
> This is one thing that comes to mind.
> Lazy-preempt should have been fixed in -rt3, too. This should not give
> you higher latencies but higher throughput.
> 
> What about rt4? It is only the stable update so you should see here the
> numbers from rt3. If that is true and your numbers are stable it should
> be easy to run git bisect between rt4 and rt5. And looking at
>   https://git.kernel.org/rt/linux-rt-devel/h/v4.4.1-rt5
> the only non-cosmetic change in -rt5 that should affect you is the
> migrate-disable fixup from Mike.
Ok, each run takes a couple of hours so bisecting should take quite some time
but i will give it a try. I started a test with 4.4.1-rt4, if the numbers are 
within the 70µs ballpark bisecting seems the way to go. If the numbers are 
higher i suspect that stable update might have a play here. But we will see.

Best regards
Tim