linux-kernel - Re: [RFC 2/2] Introduce sysctl(s) for the migration costs

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Message-ID: <1518198609.26824.43.camel@gmx.de>
Date:   Fri, 09 Feb 2018 18:50:09 +0100
From:   Mike Galbraith <efault@....de>
To:     Steven Sistare <steven.sistare@...cle.com>,
        Rohit Jain <rohit.k.jain@...cle.com>,
        linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, joelaf@...gle.com,
        jbacik@...com, riel@...hat.com, juri.lelli@...hat.com,
        dhaval.giani@...cle.com
Subject: Re: [RFC 2/2] Introduce sysctl(s) for the migration costs

On Fri, 2018-02-09 at 12:33 -0500, Steven Sistare wrote:
> On 2/9/2018 12:08 PM, Mike Galbraith wrote:
> 
> > Shrug.  It's bogus no mater what we do.  Once Upon A Time, a cost
> > number was generated via measurement, but the end result was just as
> > bogus as a number pulled out of the ether.  How much bandwidth you have
> > when blasting data to/from wherever says nothing about misses you avoid
> > vs those you generate.
> 
> Yes, yes and yes. I cannot make the original tunable less bogus.  Using a smaller
> cost for closer caches still makes logical sense and is supported by the data.

You forgot to write "microscopic" before "data" :)  I'm mostly agnostic
about this, but don't like the yet more knobs that 99.99% won't touch.

	-Mike