Message-ID: <3FFD7340.7050209@cyberone.com.au>
Date: Fri, 09 Jan 2004 02:12:00 +1100
From: Nick Piggin <piggin@cyberone.com.au>
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To: dipankar@in.ibm.com
CC: linux-kernel@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
       Paul McKenney <paul.mckenney@us.ibm.com>
Subject: Re: [patch] RCU for low latency [1/2]
References: <20040108114851.GA5128@in.ibm.com> <20040108114958.GB5128@in.ibm.com>
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Dipankar Sarma wrote:

>Provide a rq_has_rt_task() interface to detect runqueues with
>real time priority tasks. Useful for RCU optimizations.
>

Can you make rq_has_rt_task the slow path? Adding things like this
can actually be noticable on microbenchmarks (eg. pipe based ctx
switching). Its probably cache artifacts that I see, but it wouldn't
hurt to keep the scheduler as tight as possible.

I think this should cover it.

int rq_has_rt_task(int cpu)
{
	runqueue_t *rq = cpu_rq(cpu);
	return (sched_find_first_bit(rq->active) < MAX_RT_PRIO);
}

Any good?


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