linux-kernel - Re: [PATCH v3 0/3] cpu: pseries: Cpu offline states framework

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 25 Sep 2009 16:48:40 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	"Darrick J. Wong" <djwong@...ibm.com>
Subject: Re: [PATCH v3 0/3] cpu: pseries: Cpu offline states framework

On Thu, 2009-09-24 at 10:51 +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2009-09-15 at 14:11 +0200, Peter Zijlstra wrote:
> > I still think its a layering violation... its the hypervisor manager
> > that should be bothered in what state an off-lined cpu is in. 
> > 
> That's not how our hypervisor works.

Then fix it?

> If you ask through the management interface, to remove a CPU from a
> partition, the HV will communicate with a daemon inside the partition
> that will then unplug the CPU via the right call.
> 
> I don't really understand your objections to be honest. And I fail to
> see why it would be a layering violation to have the ability for the OS
> to indicate in what state it wishes to relinguish a CPU to the
> hypervisor, which more or less defines what is the expected latency for
> getting it back later on.

OK, so the main objection is the abuse of CPU hotplug as resource
management feature.

CPU hotplug is terribly invasive and expensive to the kernel, doing
hotplug on a minute basis is just plain crazy.

If you want a CPU in a keep it near and don't hand it back to the HV
state, why not use cpusets to isolate it and simply not run tasks on it?

cpusets don't use stopmachine and are much nicer to the rest of the
kernel over-all.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/