linux-kernel - Re: [PATCH] sched: fix env->src

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Date:	Wed, 13 Feb 2013 08:54:50 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Damien Wyart <damien.wyart@...il.com>
Cc:	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	peterz@...radead.org, mingo@...nel.org
Subject: Re: [PATCH] sched: fix env->src_cpu for active migration

Hi Damien,

Thanks for the test and the feedback.
Could you send me the sched_domain configuration of your machine with
the kernel that boots on your machine ?
It's available in /proc/sys/kernel/sched_domain/cpu*/

This should not have any impact on your machine but it looks like it have one.

Regards,
Vincent


On 13 February 2013 07:18, Damien Wyart <damien.wyart@...il.com> wrote:
> Hi,
>
> I tested this on top of 3.8-rc7 and this made the machine (x86_64, Core
> i7 920) unable to boot (very early as nothing at all is displayed on
> screen). Nothing in the kernel log (after booting with a working
> kernel).
>
> Double-checked by just backing out only this patch and this made the
> machine boot again.
>
> Damien
>
>> need_active_balance uses env->src_cpu which is set only if there is more
>> than 1 task on the run queue. We must set the src_cpu field unconditionnally
>> otherwise the test "env->src_cpu > env->dst_cpu" will always fail if there is
>> only 1 task on the run queue
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
>>  kernel/sched/fair.c |    6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 81fa536..32938ea 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5044,6 +5044,10 @@ redo:
>>
>>       ld_moved = 0;
>>       lb_iterations = 1;
>> +
>> +     env.src_cpu   = busiest->cpu;
>> +     env.src_rq    = busiest;
>> +
>>       if (busiest->nr_running > 1) {
>>               /*
>>                * Attempt to move tasks. If find_busiest_group has found
>> @@ -5052,8 +5056,6 @@ redo:
>>                * correctly treated as an imbalance.
>>                */
>>               env.flags |= LBF_ALL_PINNED;
>> -             env.src_cpu   = busiest->cpu;
>> -             env.src_rq    = busiest;
>>               env.loop_max  = min(sysctl_sched_nr_migrate, busiest->nr_running);
>>
>>               update_h_load(env.src_cpu);
--
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