From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Jason Low <jason.low2@hp.com>
Cc: Wanpeng Li <wanpeng.li@linux.intel.com>,
Preeti U Murthy <preeti@linux.vnet.ibm.com>,
peterz@infradead.org, mingo@kernel.org, riel@redhat.com,
daniel.lezcano@linaro.org, vincent.guittot@linaro.org,
pjt@google.com, benh@kernel.crashing.org, efault@gmx.de,
linux-kernel@vger.kernel.org, iamjoonsoo.kim@lge.com,
svaidy@linux.vnet.ibm.com, tim.c.chen@linux.intel.com,
morten.rasmussen@arm.com
Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs
Date: Fri, 27 Mar 2015 11:09:07 +0530 [thread overview]
Message-ID: <20150327053907.GB6895@linux.vnet.ibm.com> (raw)
In-Reply-To: <1427432841.2788.10.camel@j-VirtualBox>
* Jason Low <jason.low2@hp.com> [2015-03-26 22:07:21]:
> On Fri, 2015-03-27 at 10:12 +0800, Wanpeng Li wrote:
> > Hi Preeti,
> > On Thu, Mar 26, 2015 at 06:32:44PM +0530, Preeti U Murthy wrote:
> > >
> > >1. An ILB CPU was chosen from the first numa domain to trigger nohz idle
> > >load balancing [Given the experiment, upto 6 CPUs per core could be
> > >potentially idle in this domain.]
> > >
> > >2. However the ILB CPU would call load_balance() on itself before
> > >initiating nohz idle load balancing.
> > >
> > >3. Given cores are SMT8, the ILB CPU had enough opportunities to pull
> > >tasks from its sibling cores to even out load.
> > >
> > >4. Now that the ILB CPU was no longer idle, it would abort nohz idle
> > >load balancing
> >
> > I don't see abort nohz idle load balancing when ILB CPU was no longer idle
> > in nohz_idle_balance(), could you explain more in details?
>
> Hi Wanpeng,
>
> In nohz_idle_balance(), there is a check for need_resched() so if the
> cpu has something to run, it should exit nohz_idle_balance(), which may
> cause it to not do the idle balancing on the other CPUs.
>
Yes, the need_resched() in nohz_idle_balance() would exit the
nohz_idle_balance if it has something to run. However I wonder if we
should move the need_resched check out of the for loop. i.e the
need_resched check should probably be there with the idle check.
With the current code when the ilb cpus are not free:
- We would be updating the nohz.next_balance even through we havent done
any load balance.
- We might iterate thro the nohz.idle_cpus_mask()s to find balance_cpus.
--
Thanks and Regards
Srikar Dronamraju
next prev parent reply other threads:[~2015-03-27 5:40 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 13:02 [PATCH V2] sched: Improve load balancing in the presence of idle CPUs Preeti U Murthy
2015-03-26 17:03 ` Jason Low
2015-03-27 2:12 ` Wanpeng Li
2015-03-27 4:33 ` Preeti U Murthy
2015-03-27 4:23 ` Wanpeng Li
2015-03-27 5:01 ` Jason Low
2015-03-27 5:07 ` Jason Low
2015-03-27 5:39 ` Srikar Dronamraju [this message]
2015-03-27 7:00 ` Wanpeng Li
2015-03-27 6:43 ` Wanpeng Li
2015-03-27 16:23 ` Preeti U Murthy
2015-03-27 11:43 ` [tip:sched/core] " tip-bot for Preeti U Murthy
2015-03-27 13:03 ` [PATCH V2] " Srikar Dronamraju
2015-03-27 14:38 ` Morten Rasmussen
2015-03-27 16:46 ` Preeti U Murthy
2015-03-27 17:56 ` Morten Rasmussen
2015-03-30 7:26 ` Preeti U Murthy
2015-03-30 11:30 ` Morten Rasmussen
2015-03-30 11:06 ` Peter Zijlstra
2015-03-30 12:03 ` Morten Rasmussen
2015-03-30 12:24 ` Peter Zijlstra
2015-03-30 12:54 ` Peter Zijlstra
2015-03-30 13:29 ` Vincent Guittot
2015-03-30 14:01 ` Peter Zijlstra
2015-03-30 15:27 ` Morten Rasmussen
2015-03-31 8:58 ` Preeti U Murthy
2015-03-31 17:30 ` Jason Low
2015-04-01 6:28 ` Preeti U Murthy
2015-04-01 13:03 ` Morten Rasmussen
2015-04-02 0:55 ` Jason Low
2015-04-02 3:22 ` Preeti U Murthy
2015-03-30 13:45 ` Vincent Guittot
2015-03-31 8:06 ` Preeti U Murthy
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