linux-kernel - Re: Make yield_task

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Message-ID: <20080221090430.GA20055@elte.hu>
Date:	Thu, 21 Feb 2008 10:04:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Peter Zijlstra <peter@...gramming.kicks-ass.net>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Subject: Re: Make yield_task_fair more efficient


* Balbir Singh <balbir@...ux.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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