linux-kernel - Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq

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: <53296AD0.5090908@linux.vnet.ibm.com>
Date:	Wed, 19 Mar 2014 15:30:48 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Dirk Brandewie <dirk.brandewie@...il.com>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Patrick Marlier <patrick.marlier@...il.com>
Subject: Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq_driver interface.

On 03/19/2014 10:33 AM, Viresh Kumar wrote:
> On 18 March 2014 17:46, Srivatsa S. Bhat
> <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>> Agreed. As far as I understand, for ->target drivers, today we use GOV_STOP
>> to stop managing the CPU going offline. And for ->setpolicy drivers, we will
>> use this new callback to achieve the same goal.
> 
> So a better question would be: What's the purpose of ->stop() call for a policy?

Ideally, it should remove the outgoing CPU from the policy and "stop managing
that CPU", whatever that means to the driver (for intel_pstate, it means
setting it to min P state and destroying the timer).

> Stop managing CPUs of that policy?

Stop managing only the particular CPU going offline. IOW, we should somehow
communicate to the ->stop() callback that we are taking CPU 'x' offline.

If adding a ->stop() callback in the cpufreq_driver is not the best way to
achieve it, then lets think of an alternative. The way I look at it, this
new mechanism what we want, should allow ->setpolicy drivers to do what the
GOV_STOP will do for regular drivers. That is, allow it to "shutdown the
CPU from a cpufreq perspective", whatever that means to the driver.
We can think of a completely different way of achieving it, if ->stop()
is not suitable for that purpose.

> Or even do something on CPUs of a policy
> before CPUs are offlined?
> 
> Probably in the current solution Dirk is doing both these things..
> 
> And so I thought maybe its better not to restrict ->stop() to just
> setpolicy() drivers.

Regards,
Srivatsa S. Bhat

--
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/