linux-kernel - Re: [PATCH] clockevents: Leave broadcast device shtudown only if the current device is always running.

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: <CAMQu2gwkGjWgLN3FVkzqeYCA+N-+==HPnjmH68AKgBsYrKtXaw@mail.gmail.com>
Date:	Tue, 10 Apr 2012 12:26:43 +0530
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	johnstul@...ibm.com
Subject: Re: [PATCH] clockevents: Leave broadcast device shtudown only if the
 current device is always running.

On Tue, Apr 10, 2012 at 4:11 AM, Suresh Siddha
<suresh.b.siddha@...el.com> wrote:
> On Mon, 2012-04-09 at 11:33 +0530, Santosh Shilimkar wrote:
>> Commit 77b0d60{clockevents: Leave the broadcast device in shutdown mode
>> when not needed} was intended to leave the broadcast device in shutdown mode
>> when the per-cpu clockevent devices are always running.
>>
>> This breaks the systems where per cpu clock events stop in low power states.
>>
>> Hence revert 77b0d60 and implement the same requirement with use
>> of C3STOP feature flag.
>
> Problem you encountered is not related to leaving the broadcast device
> in shutdown mode. Problem is that we didn't track the mode change to
> oneshot and later during idle entry/exit, when we request the broadcast
> device services using CLOCK_EVT_NOTIFY_BROADCAST_ENTER etc,
> tick_broadcast_oneshot_control() returns with out doing much as it
> thinks broadcast device is in periodic mode.
>
You are right. In my last traces I didn't track the broadcast device state
fully. Did some more tracing and indeed the issue was the broadcast
device mode.

> Can you please check if the appended patch fixes the issue? I could
> reproduce the issue on my NHM platform which doesn't have always running
> apic timer and with the appended fix, all is well with cpu's going into
> tickless idle etc. Thanks.
> ---
>
Yes it does work on OMAP too.

> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: clockevents: track broadcast device mode change in tick_broadcast_switch_to_oneshot()
>
> In the commit 77b0d60c5adf39c74039e2142a1d3cd1e4d53799,
> "clockevents: Leave the broadcast device in shutdown mode when not needed",
> we were bailing out too quickly in tick_broadcast_switch_to_oneshot(),
> with out tracking the broadcast device mode change to 'TICKDEV_MODE_ONESHOT'.
>
> This breaks the platforms which need broadcast device oneshot services during
> deep idle states. tick_broadcast_oneshot_control() thinks that it is
> in periodic mode and fails to take proper decisions based on the
> CLOCK_EVT_NOTIFY_BROADCAST_[ENTER, EXIT] notifications during deep
> idle entry/exit.
>
> Fix this by tracking the broadcast device mode as 'TICKDEV_MODE_ONESHOT',
> before leaving the broadcast HW device in shutdown mode if there are no active
> requests for the moment.
>
> Reported-by: Santosh Shilimkar <santosh.shilimkar@...com>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
Thanks for the patch. Feel free to add,
Tested-by: Santosh Shilimkar <santosh.shilimkar@...com>	

Regards
Santosh
--
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/