Date: Thu, 21 Feb 2008 10:04:30 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Peter Zijlstra <peter@programming.kicks-ass.net>,
       Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
       Dhaval Giani <dhaval@linux.vnet.ibm.com>, linux-kernel@vger.kernel.org,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Subject: Re: Make yield_task_fair more efficient
Message-ID: <20080221090430.GA20055@elte.hu>
References: <20080221053321.GA26918@balbir.in.ibm.com> <20080221060427.GA9159@elte.hu> <47BD1F75.5030506@linux.vnet.ibm.com> <20080221070733.GA13694@elte.hu> <47BD2A99.3010608@linux.vnet.ibm.com> <1203583439.6243.119.camel@lappy> <47BD3B56.3090404@linux.vnet.ibm.com>
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* Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> If you insist that sched_yield() is bad, I might agree, but how does 
> my patch make things worse. [...]

it puts new instructions into the hotpath.

> [...] In my benchmarks, it has helped the sched_yield case, why is 
> that bad? [...]

I had the same cache for the rightmost task in earlier CFS (it's a 
really obvious thing) but removed it. It wasnt a bad idea, but it hurt 
the fastpath hence i removed it. Algorithms and implementations are a 
constant balancing act.

	Ingo
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