linux-kernel - Re: balance storm

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Message-ID: <5385368E.2060507@huawei.com>
Date:	Wed, 28 May 2014 09:06:22 +0800
From:	Libo Chen <libo.chen@...wei.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Mike Galbraith <umgwanakikbuti@...il.com>, <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Li Zefan" <lizefan@...wei.com>, <peterz@...radead.org>,
	Huang Qiang <h.huangqiang@...wei.com>
Subject: Re: balance storm

On 2014/5/28 4:53, Thomas Gleixner wrote:
> On Tue, 27 May 2014, Libo Chen wrote:
>> On 2014/5/27 17:55, Mike Galbraith wrote:
>>> On Tue, 2014-05-27 at 15:56 +0800, Libo Chen wrote: 
>>>>> On 2014/5/26 22:19, Mike Galbraith wrote:
>>>>>>> On Mon, 2014-05-26 at 20:16 +0800, Libo Chen wrote: 
>>>>>>>>> On 2014/5/26 13:11, Mike Galbraith wrote:
>>>>>>>
>>>>>>>>>>> Your synthetic test is the absolute worst case scenario.  There has to
>>>>>>>>>>> be work between wakeups for select_idle_sibling() to have any chance
>>>>>>>>>>> whatsoever of turning in a win.  At 0 work, it becomes 100% overhead.
>>>>>>>>>
>>>>>>>>> not synthetic, it is a real problem in our product. under no load, waste
>>>>>>>>> much cpu time.
>>>>>>>
>>>>>>> What happens in your product if you apply the commit I pointed out?
>>>>>
>>>>> under no load, cpu usage is up to 60%, but the same apps cost 10% on
>>>>> susp sp1.  The apps use a lot of timer.
>>> Something is rotten.  3.14-rt contains that commit, I ran your test with
>>> 256 threads on 64 core box, saw ~4%.
>>>
>>> Putting master/nopreempt config on box and doing the same test, box is
>>> chewing up truckloads of CPU, but not from migrations. 
>>>
>>> perf top -g --sort=symbol
>> in my box:
>>
>> perf top -g --sort=symbol
>>
>> Events: 3K cycles
>>  73.27%  [k] read_hpet
> 
> Why is that machine using read_hpet() ?
> 
> Please provide the output of 
> 
> # dmesg | grep -i tsc
> 

Euler:/home # dmesg  | grep -i tsc
[    0.000000] Fast TSC calibration using PIT
[    0.226921] TSC synchronization [CPU#0 -> CPU#1]:
[    0.227142] Measured 1053728 cycles TSC warp between CPUs, turning off TSC clock.
[    0.008000] Marking TSC unstable due to check_tsc_sync_source failed

> and
> 
> # cat /sys/devices/system/clocksource/clocksource0/available_clocksource

hpet acpi_pm

> 
> and
> 
> # cat /sys/devices/system/clocksource/clocksource0/current_clocksource

hpet

> 
> Thanks,
> 
> 	tglx
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