linux-kernel - Re: [PATCH v2 0/2] cpu: pseries: Offline state 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]

Message-ID: <20090902200214.GA1918@ucw.cz>
Date:	Wed, 2 Sep 2009 22:02:14 +0200
From:	Pavel Machek <pavel@....cz>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	"Darrick J. Wong" <djwong@...ibm.com>
Subject: Re: [PATCH v2 0/2] cpu: pseries: Offline state framework.

On Wed 2009-09-02 07:33:31, Peter Zijlstra wrote:
> On Fri, 2009-08-28 at 15:30 +0530, Gautham R Shenoy wrote:
> > Hi,
> > 
> > This is the version 2 of the patch series to provide a cpu-offline framework
> > that enables the administrators choose the state the offline CPU must be put
> > into when multiple such states are exposed by the underlying architecture.
> > 
> > Version 1 of the Patch can be found here:
> > http://lkml.org/lkml/2009/8/6/236
> > 
> > The patch-series exposes the following sysfs tunables to
> > allow the system-adminstrator to choose the state of a CPU:
> > 
> > To query the available hotplug states, one needs to read the sysfs tunable:
> > 	/sys/devices/system/cpu/cpu<number>/available_hotplug_states
> > To query or set the current state, on needs to read/write the sysfs tunable:
> > 	/sys/devices/system/cpu/cpu<number>/current_states
> > 
> > The patchset ensures that the writes to the "current_state" sysfs file are
> > serialized against the writes to the "online" file.
> > 
> > This patchset also contains the offline state driver implemented for
> > pSeries. For pSeries, we define three available_hotplug_states. They are:
> > 
> > 	online: The processor is online.
> > 
> > 	deallocate: This is the the default behaviour when the cpu is offlined
> > 	even in the absense of this driver. The CPU would call make an
> > 	rtas_stop_self() call and hand over the CPU back to the resource pool,
> > 	thereby effectively deallocating that vCPU from the LPAR.
> > 	NOTE: This would result in a configuration change to the LPAR
> > 	which is visible to the outside world.
> > 
> > 	deactivate: This cedes the vCPU to the hypervisor which
> > 	in turn can put the vCPU time to the best use.
> > 	NOTE: This option DOES NOT result in a configuration change
> > 	and the vCPU would be still entitled to the LPAR to which it earlier
> > 	belong to.
> > 
> > Awaiting your feedback.
> 
> I'm still thinking this is a bad idea.
> 
> The OS should only know about online/offline.
> 
> Use the hypervisor interface to deal with the cpu once its offline.
> 
> That is, I think this interface you propose is a layering violation.

Agreed. Plus having interface like 'go to this state during offliine'
then 'go offline' is strange/stupid. For hypervisor case, you might
want to change 'state' of cpu that is already offline.
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--
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/