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]

Date:	Thu, 6 Aug 2009 19:18:44 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Joel Schopp <jschopp@...tin.ibm.com>,
	"Brown, Len" <len.brown@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Balbir Singh <balbir@...ibm.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...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.

Hi Shaohua,

On Thu, Aug 06, 2009 at 09:58:55AM +0800, Shaohua Li wrote:
> Hi,
> 
> On Wed, Aug 05, 2009 at 10:25:53PM +0800, Gautham R Shenoy wrote:
> > In this patch-series, we propose to extend the CPU-Hotplug infrastructure
> > and allow the system administrator to choose the desired state the CPU should
> > go to when it is offlined. We think this approach addresses the concerns about
> > determinism as well as transparency, since CPU-Hotplug already provides
> > notification mechanism which the userspace can listen to for any change
> > in the configuration and correspondingly readjust any previously set
> > cpu-affinities.
> Peter dislikes any approach (including cpuhotplug) which breaks userspace policy,
> even userspace can get a notification.

I think Peter's problem was more to do with the kernel offlining the CPUs
behind the scenes, right ?

We don't do that in this patch series. The option to offline the CPUs is
very much with the admin. The patch-series only provides the interface
that helps the admin choose the state the CPU must reside in when it
goes offline.

> 
> > Also, approaches such as [1] can make use of this
> > extended infrastructure instead of putting the CPU to an arbitrary C-state
> > when it is offlined, thereby providing the system administrator a rope to hang
> > himself with should he feel the need to do so.
> I didn't see the reason why administrator needs to know which state offline cpu
> should stay. Don't know about powerpc side, but in x86 side, it appears deepest
> C-state is already preferred.

We can still provide a sane default value based on what states are
available and what the BIOS limits us to. Thus we can still use the
idle-state-offline patch that Venki posted sometime ago, right ?

> 
> Thanks,
> Shaohua

-- 
Thanks and Regards
gautham
--
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/