Re: [RFC] [PATCH 1/1] hrtimers: Cache next hrtimer

From: Ashwin Chaugule <ashwinc@codeaurora.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com
Subject: Re: [RFC] [PATCH 1/1] hrtimers: Cache next hrtimer
Date: Mon, 31 Aug 2009 23:13:39 -0400	[thread overview]
Message-ID: <4A9C9163.50907@codeaurora.org> (raw)
In-Reply-To: <alpine.LFD.2.00.0908310854020.19335@localhost.localdomain>

Thomas Gleixner wrote:

>> This looks very good ! Our results are almost similar now. However, I think
>> that with this new
>> patch we're still arming the timer needlessly at least once. This is the
>> case when we're trying to remove the first (oldest) hrtimer with
>> timer->expires = cpu->expires_next, but we forgo the reprogramming, when we
>> really shouldn't. At this point, with the current scheme of things, we will
>> needlessly wakeup and simply correct the expires_next value by
>> traversing up the rbtree, to the parent node.
>>     
>
> That only happens, when that timer is the last one in both trees. Then
> the resulting reprogramming value is KTIME_MAX and we skip the
> reprogramming. That's easy to fix by removing the KTIME_MAX check.
>  
>   
Hmm. Agreed. I'll fix this and send a patch in the next few days. Otherwise, I think all else looks good.

Cheers,
Ashwin