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SubjectRe: Fix bug: Scheduler's idle-load-balancer not running in first 5 mins after bootup
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On Mon, 2012-01-30 at 10:14 -0800, Diwakar Tundlam wrote:
> 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@nvidia.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@nvidia.com>
> Reviewed-by: Aleksandr Frid <afrid@nvidia.com>
> Reviewed-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
> Reviewed-by: Satya Popuri <spopuri@nvidia.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)

Shouldn't that really be INITIAL_JIFFIES + HZ?

-Mike



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