linux-kernel - Fix bug: Scheduler's idle-load-balancer not running in first 5 mins after bootup

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Message-ID: <1DD7BFEDD3147247B1355BEFEFE466523791832BD5@HQMAIL04.nvidia.com>
Date:	Mon, 30 Jan 2012 10:14:23 -0800
From:	Diwakar Tundlam <dtundlam@...dia.com>
To:	'Ingo Molnar' <mingo@...e.hu>,
	'Peter Zijlstra' <peterz@...radead.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
CC:	Peter De Schrijver <pdeschrijver@...dia.com>,
	Antti Miettinen <amiettinen@...dia.com>,
	Matthew Longnecker <MLongnecker@...dia.com>,
	Kevin Kranzusch <KKranzusch@...dia.com>
Subject: Fix bug: Scheduler's idle-load-balancer not running in first 5 mins
 after bootup

We ran into this at Nvidia. QA filed a bug saying coremark_4pthreads scores lower (as if running on 3 cores) when run shortly after bootup. But later its score increases to expected values on 4 cores.

This patch is relevant to linux-2.6.39 but I noticed this fix is not made in linux-3.0, 3.1, 3.2 or 3.3 also.

Please see commit log for more details of the problem and fix.

Thanks,
  Diwakar.
  Tegra Android Kernel SW Engg.
  NVIDIA.
  Santa Clara, CA

commit d04d7ef0e3f8c70bd6cd5abb2abc0236aa8d1f7c
Author: Diwakar Tundlam <dtundlam@...dia.com>
Date:   Wed Jan 18 18:58:57 2012 -0800

    scheduler: domain: init next_balance in nohz_idle_balancer with jiffies
    
    The next_balance parameter of nohz_idle_balancer should be initialized
    to jiffies since jiffies itself is initialized to 300 seconds shy of
    overflow. Otherwise, nohz_idle_balancer does not run for the first 5
    mins after bootup.
    
    Signed-off-by: Diwakar Tundlam <dtundlam@...dia.com>
    Reviewed-by: Aleksandr Frid <afrid@...dia.com>
    Reviewed-by: Peter Boonstoppel <pboonstoppel@...dia.com>
    Reviewed-by: Satya Popuri <spopuri@...dia.com>

 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c index c5b09f7..506c5da 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8288,6 +8288,7 @@ void __init sched_init(void)
        atomic_set(&nohz.load_balancer, nr_cpu_ids);
        atomic_set(&nohz.first_pick_cpu, nr_cpu_ids);
        atomic_set(&nohz.second_pick_cpu, nr_cpu_ids);
+       nohz.next_balance = jiffies;
 #endif
        /* May be allocated at isolcpus cmdline parse time */
        if (cpu_isolated_map == NULL)
--
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