linux-kernel - Re: [PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt

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Date:	Tue, 5 Feb 2013 11:37:14 +0800
From:	Honghui Zhang <zhanghonghui@...wei.com>
To:	Kirill Tkhai <tkhai@...dex.ru>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: Decrease number of calls of push_rt_task()
 in push_rt_tasks()

On 2013/2/1 5:57, Kirill Tkhai wrote:
> 
> 
> 31.01.2013, 20:08, "Steven Rostedt" <rostedt@...dmis.org>:
>> On Mon, 2013-01-28 at 03:46 +0400, Kirill Tkhai wrote:
>>
>>>  The patch aims to decrease the number of calls of push_rt_task()
>>>  in push_rt_tasks().
>>>
>>>  It's not necessary to push more than 'num_online_cpus() - 1' tasks.
>>>  If just pushed task doesn't leave its new CPU during our local call
>>>  of push_rt_tasks() than we won't push another task to the CPU.
>>>  If it leave or change priority than it will pull new task by itself.
>>
>> I'm curious. Have you hit situations where this was an issue? Or was
>> this just discovered by code review?
> 
> No, I did't hit this situation. It's impossible to hook every situation.
> 
> Thanks for your explanation.
> 
> Kirill
> 

Suppose we have a large number of cpus(say 4096), with the last one running
a low-priority task on it. Is it possible with this patch we will never reach
the last cpu in case that previous cpu has complete the pulled task?


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