linux-kernel - Re: [PATCH 0/3] cpu: idle state framework for offline CPUs.

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: <20090814113021.GL32418@elf.ucw.cz>
Date:	Fri, 14 Aug 2009 13:30:21 +0200
From:	Pavel Machek <pavel@....cz>
To:	Dipankar Sarma <dipankar@...ibm.com>
Cc:	Len Brown <lenb@...nel.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	"Brown, Len" <len.brown@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Balbir Singh <balbir@...ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	"Darrick J. Wong" <djwong@...ibm.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] cpu: idle state framework for offline CPUs.

> > > 2. A low-power state where the guest indicates it doesn't need the
> > > CPU (and can be put in low power state) but doesn't want to give up 
> > > its allocated cpu share. IOW, no visible configuration changes.
> > > 
> > > So, in any case we would probably want more than one states.
> > 
> > How are #1 and #2 different when the hypervisor
> > gets control in all idle states?  I assert that
> > they are the same, and thus 1 state will suffice.
> 
> It depends on the hypervisor implementation. On pseries (powerpc)
> hypervisor, for example, they are different. By offlining a vcpu
> (and in turn shutting a cpu), you will actually create a configuration
> change in the VM that is visible to other systems management tools
> which may not be what the system administrator wanted. Ideally,
> we would like to distinguish between these two states.
> 
> Hope that suffices as an example.

So... you have something like "physically pulling out hotplug cpu" on
powerpc.

But maybe it is useful to take already offline cpus (from linux side),
and make that visible to hypervisor, too.

So maybe something like "echo 1 > /sys/devices/system/cpu/cpu1/unplug"
would be more useful for hypervisor case?

-- 
(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/