From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Willy Tarreau <willy@w.ods.org>
Subject: Re: interactive task starvation
Date: Tue, 21 Mar 2006 22:47:30 +0100
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Cc: Con Kolivas <kernel@kolivas.org>, Mike Galbraith <efault@gmx.de>,
       Ingo Molnar <mingo@elte.hu>, lkml <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, bugsplatter@gmail.com
References: <1142592375.7895.43.camel@homer> <200603211939.12749.rjw@sisk.pl> <20060321193216.GA27753@w.ods.org>
In-Reply-To: <20060321193216.GA27753@w.ods.org>
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On Tuesday 21 March 2006 20:32, Willy Tarreau wrote:
> On Tue, Mar 21, 2006 at 07:39:11PM +0100, Rafael J. Wysocki wrote:
> > On Tuesday 21 March 2006 15:39, Willy Tarreau wrote:
> > > On Wed, Mar 22, 2006 at 01:19:49AM +1100, Con Kolivas wrote:
> > > > On Wednesday 22 March 2006 01:17, Mike Galbraith wrote:
> > > > > On Wed, 2006-03-22 at 00:53 +1100, Con Kolivas wrote:
> > > > > > The yardstick for changes is now the speed of 'ls' scrolling in the
> > > > > > console. Where exactly are those extra cycles going I wonder? Do you
> > > > > > think the scheduler somehow makes the cpu idle doing nothing in that
> > > > > > timespace? Clearly that's not true, and userspace is making something
> > > > > > spin unnecessarily, but we're gonna fix that by modifying the
> > > > > > scheduler.... sigh
> > > > >
> > > > > *Blink*
> > > > >
> > > > > Are you having a bad hair day??
> > > > 
> > > > My hair is approximately 3mm long so it's kinda hard for that to happen. 
> > > > 
> > > > What you're fixing with unfairness is worth pursuing. The 'ls' issue just 
> > > > blows my mind though for reasons I've just said. Where are the magic cycles 
> > > > going when nothing else is running that make it take ten times longer?
> > > 
> > > Con, those cycles are not "magic", if you look at the numbers, the time is
> > > not spent in the process itself. From what has been observed since the
> > > beginning, it is spent :
> > >   - in other processes which are starvating the CPU (eg: X11 when xterm
> > >     scrolls)
> > >   - in context switches when you have a pipe somewhere and the CPU is
> > >     bouncing between tasks.
> > > 
> > > Concerning your angriness about me being OK with (0,0) and still
> > > asking for tunables, it's precisely because I know that *my* workload
> > > is not everyone else's, and I don't want to conclude too quickly that
> > > there are only two types of workloads.
> > 
> > Well, perhaps we can assume there are only two types of workloads and
> > wait for a test case that will show the assumption is wrong?
> 
> It would certainly fit most usages, but as soon as we find another group
> of users complaining, we will add another sysctl just for them ? Perhaps
> we could just resume the two current sysctls into one called
> "interactivity_boost" with a value between 0 and 100, with the ability
> for any user to increase or decrease it easily ? Mainline would be
> pre-configured with something reasonable, like what Mike proposed as
> default values for example, and server admins would only set it to
> zero while desktop-intensive users could increase it a bit if they like
> to.

Sounds reasonable to me.

Greetings,
Rafael
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