linux-kernel - Re: [RFC] Dynamic Tick and Deferrable Timer Support

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Message-Id: <20090114221624.76ee8aa4.akpm@linux-foundation.org>
Date:	Wed, 14 Jan 2009 22:16:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Hunter, Jon" <jon-hunter@...com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Subject: Re: [RFC] Dynamic Tick and Deferrable Timer Support

On Wed, 14 Jan 2009 14:03:09 -0600 "Hunter, Jon" <jon-hunter@...com> wrote:

> Hello All,
> 
> I have been working to maximise the kernel sleep time on an embedded device by utilising the dynamic tick and deferrable timer features.
> 
> During the course of this work I found that although timers were configured as deferrable, only timers for time interval tv1 were actually being deferred. Reviewing the deferrable timer patch [1], it does appear that the code is written to only defer timers for interval tv1. Therefore, I wanted to ask if this is intentional or not?
> 
> I have applied the below patch to defer all deferrable timers regardless of interval and so far it is working on the embedded device. I wanted to share this in case this could be something that could be applied to the mainline.
> 
> Please excuse any foolish mistakes I may have made here as this is my first post to your mailing list. Any feedback you could offer would be appreciated.
> 
> Cheers
> Jon
> 
> [1] Deferrable timer patch: http://marc.info/?l=linux-kernel&m=117512286417320&w=2
> 
> 
> Signed-off-by: Jon Hunter <jon-hunter@...com>
> ---
>  kernel/timer.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index dee3f64..76a3ac6 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -930,6 +930,9 @@ cascade:
>                 index = slot = timer_jiffies & TVN_MASK;
>                 do {
>                         list_for_each_entry(nte, varp->vec + slot, entry) {
> +                               if (tbase_get_deferrable(nte->base))
> +                                       continue;
> +
>                                 found = 1;
>                                 if (time_before(nte->expires, expires))
>                                         expires = nte->expires;

Venki, could you please take a look?
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