linux-kernel - Re: [PATCH 5/9] x86/intel_rdt: Add new cgroup and Class of service management

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Message-ID: <20150805161029.GM17598@mtj.duckdns.org>
Date:	Wed, 5 Aug 2015 12:10:29 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Vikas Shivappa <vikas.shivappa@...el.com>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
	tglx@...utronix.de, mingo@...nel.org, peterz@...radead.org,
	matt.fleming@...el.com, will.auld@...el.com,
	glenn.p.williamson@...el.com, kanaka.d.juvva@...el.com
Subject: Re: [PATCH 5/9] x86/intel_rdt: Add new cgroup and Class of service
 management

Hello,

On Wed, Aug 05, 2015 at 01:22:57PM +0100, Matt Fleming wrote:
> I wager that this assertion is wrong. Having individual applications
> program their own cache mask is not going to be the most common
> scenario. Only in very specific situations would you trust an
> application to do that.

As I wrote in the other reply, I don't buy that.  The above only holds
if you exclude use cases where this feature is used by multiple
threads of an application and I can't see a single reason why such
uses would be excluded.

> A much more likely use case is having the sysadmin carve up the cache
> for a workload which may include multiple, uncooperating applications.
> 
> Yes, a programmable interface would be useful, but only for a limited
> set of workloads. I don't think it's how most people are going to want
> to use this hardware technology.

It's actually the other way around.  You can achieve most of what
cgroups can do with programmable interface albeit with some
awkwardness.  The other direction is a lot more heavier and painful.

Thanks.

-- 
tejun
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