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Date: Mon, 09 Sep 2013 13:40:33 -0700 From: Jason Low <jason.low2@...com> To: Peter Zijlstra <peterz@...radead.org> Cc: mingo@...hat.com, linux-kernel@...r.kernel.org, efault@....de, pjt@...gle.com, preeti@...ux.vnet.ibm.com, akpm@...ux-foundation.org, mgorman@...e.de, riel@...hat.com, aswin@...com, scott.norton@...com, srikar@...ux.vnet.ibm.com Subject: Re: [RFC][PATCH v4 3/3] sched: Periodically decay max cost of idle balance On Mon, 2013-09-09 at 13:44 +0200, Peter Zijlstra wrote: > On Tue, Sep 03, 2013 at 11:02:59PM -0700, Jason Low wrote: > > On Fri, 2013-08-30 at 12:29 +0200, Peter Zijlstra wrote: > > > rcu_read_lock(); > > > for_each_domain(cpu, sd) { > > > + /* > > > + * Decay the newidle max times here because this is a regular > > > + * visit to all the domains. Decay ~0.5% per second. > > > + */ > > > + if (time_after(jiffies, sd->next_decay_max_lb_cost)) { > > > + sd->max_newidle_lb_cost = > > > + (sd->max_newidle_lb_cost * 254) / 256; > > > > I initially picked 0.5%, but after trying it out, it appears to decay very > > slowing when the max is at a high value. Should we increase the decay a > > little bit more? Maybe something like: > > > > sd->max_newidle_lb_cost = (sd->max_newidle_lb_cost * 63) / 64; > > So the half-life in either case is is given by: > > n = ln(1/2) / ln(x) > > which gives 88 seconds for x := 254/256 or 44 seconds for x := 63/64. > > I don't really care too much, but obviously something like: > > 256*exp(ln(.5)/60) ~= 253 > > Is attractive ;-) > > > > + /* > > > + * Stop the load balance at this level. There is another > > > + * CPU in our sched group which is doing load balancing more > > > + * actively. > > > + */ > > > + if (!continue_balancing) { > > > > Is "continue_balancing" named "balance" in older kernels? > > Yeah, this patch crossed paths with a series remodeling the > load-balancer a bit, that should all be pushed-out to tip/master. > > In particular see commit: > 23f0d20 sched: Factor out code to should_we_balance() > > > Here are the AIM7 results with the other 2 patches + this patch with the > > slightly higher decay value. > > Just to clarify, 'this patch' is the one I sent? Yes, I was referring to the one you sent out. Also, I did the s/smp_processor_id()/this_cpu/ on patch 2. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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