linux-kernel - Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support.

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20090617143804.GA6767@linux.vnet.ibm.com>
Date:	Wed, 17 Jun 2009 07:38:04 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	svaidy@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	linux-kernel@...r.kernel.org, Balbir Singh <balbir@...ibm.com>,
	Rusty Russel <rusty@...tcorp.com.au>,
	Nathan Lynch <ntl@...ox.com>, Ingo Molnar <mingo@...e.hu>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Shoahua Li <shaohua.li@...ux.com>
Subject: Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support.

On Wed, Jun 17, 2009 at 09:32:57AM +0200, Peter Zijlstra wrote:
> On Tue, 2009-06-16 at 13:37 +0530, Vaidyanathan Srinivasan wrote:
> > * Andrew Morton <akpm@...ux-foundation.org> [2009-06-15 23:23:18]:
> > 
> > > On Tue, 16 Jun 2009 11:08:39 +0530 Gautham R Shenoy <ego@...ibm.com> wrote:
> > > 
> > > > Currently on a ppc64 box with 16 CPUs, the time taken for
> > > > a individual cpu-hotplug operation is as follows.
> > > > 
> > > >     # time echo 0 > /sys/devices/system/cpu/cpu2/online
> > > >     real    0m0.025s
> > > >     user    0m0.000s
> > > >     sys     0m0.002s
> > > > 
> > > >     # time echo 1 > /sys/devices/system/cpu/cpu2/online
> > > >     real    0m0.021s
> > > >     user    0m0.000s
> > > >     sys     0m0.000s
> > > 
> > > Surprised.  Do people really online and offline CPUs frequently enough
> > > for this to be a problem?
> > 
> > Certainly not for hardware faults or hardware replacement, but
> > cpu-hotplug interface is useful for changing system configuration to
> > meet different objectives like
> > 
> > * Reduce system capacity to reduce average power and reduce heat
> > 
> > * Increasing number of cores and threads in a CPU package is leading
> >   to multiple cpu offline/online operations for any perceivable effect
> > 
> > * Dynamically change CPU configurations in virtualized environments
> 
> I tend to agree with Andrew, if any of those things are done frequent
> enough that the hotplug performance matter you're doing something mighty
> odd.

Boot speedup?

							Thanx, Paul
--
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/