linux-kernel - Re: [PATCH V2] cpuidle: Handle tick_broadcast

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: <1562115.g1s3BW0dJA@vostro.rjw.lan>
Date:	Thu, 07 May 2015 22:50:14 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, tglx@...utronix.de,
	rafael.j.wysocki@...el.com, daniel.lezcano@...aro.org,
	rlippert@...gle.com, linux-pm@...r.kernel.org,
	linus.walleij@...aro.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, sudeep.holla@....com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH V2] cpuidle: Handle tick_broadcast_enter() failure gracefully

On Thursday, May 07, 2015 11:17:21 PM Preeti U Murthy wrote:
> When a CPU has to enter an idle state where tick stops, it makes a call
> to tick_broadcast_enter(). The call will fail if this CPU is the
> broadcast CPU. Today, under such a circumstance, the arch cpuidle code
> handles this CPU.  This is not convincing because not only are we not
> aware what the arch cpuidle code does, but we also do not account for
> the idle state residency time and usage of such a CPU.
> 
> This scenario can be handled better by simply asking the cpuidle
> governor to choose an idle state where in ticks do not stop. To
> accommodate this change move the setting of runqueue idle state from the
> core to the cpuidle driver, else the rq->idle_state will be set wrong.
> 
> Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> ---
> Changes from V1: https://lkml.org/lkml/2015/5/7/24
> Rebased on the latest linux-pm/bleeding-edge
> 
>  drivers/cpuidle/cpuidle.c          |   21 +++++++++++++++++----
>  drivers/cpuidle/governors/ladder.c |   13 ++++++++++---
>  drivers/cpuidle/governors/menu.c   |    6 +++++-
>  include/linux/cpuidle.h            |    6 +++---
>  include/linux/sched.h              |   16 ++++++++++++++++
>  kernel/sched/core.c                |   17 +++++++++++++++++
>  kernel/sched/fair.c                |    2 +-
>  kernel/sched/idle.c                |    8 +-------
>  kernel/sched/sched.h               |   24 ------------------------
>  9 files changed, 70 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 8c24f95..b7e86f4 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -21,6 +21,7 @@
>  #include <linux/module.h>
>  #include <linux/suspend.h>
>  #include <linux/tick.h>
> +#include <linux/sched.h>
>  #include <trace/events/power.h>
>  
>  #include "cpuidle.h"
> @@ -168,10 +169,17 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>  	 * CPU as a broadcast timer, this call may fail if it is not available.
>  	 */
>  	if (broadcast && tick_broadcast_enter()) {
> -		default_idle_call();
> -		return -EBUSY;
> +		index = cpuidle_select(drv, dev, !broadcast);

No, you can't do that.

This code path may be used by suspend-to-idle and that should not call
cpuidle_select().

What's needed here seems to be a fallback mechanism like "choose the
deepest state shallower than X and such that it won't stop the tick".
You don't really need to run a full governor for that.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
--
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/