linux-kernel - Re: [PATCH] oprofile: check whether oprofile perf enabled in op_overflow

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Message-ID: <52D8A56F.1010507@huawei.com>
Date:	Fri, 17 Jan 2014 11:37:19 +0800
From:	Weng Meiling <wengmeiling.weng@...wei.com>
To:	Will Deacon <will.deacon@....com>, Robert Richter <rric@...nel.org>
CC:	"oprofile-list@...ts.sf.net" <oprofile-list@...ts.sf.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Li Zefan <lizefan@...wei.com>,
	"wangnan0@...wei.com" <wangnan0@...wei.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Huang Qiang <h.huangqiang@...wei.com>,
	"sdu.liu@...wei.com" <sdu.liu@...wei.com>
Subject: Re: [PATCH] oprofile: check whether oprofile perf enabled in op_overflow_handler()

On 2014/1/17 3:36, Will Deacon wrote:
> On Thu, Jan 16, 2014 at 11:52:45AM +0000, Robert Richter wrote:
>> (cc'ing Will)
> 
> Thanks Robert,
> 
>> The problem of too low sample periods could be solved on ARM by using
>> perf's interrupt throttling, you might play around with:
>>
>>  /proc/sys/kernel/perf_event_max_sample_rate:100000
>>
>> I am not quite sure whether this works esp. for kernel counters and

Try to lower the value of perf_event_max_sample_rate, it works. Testing
the following values:
100 500 1000 5000 10000 50000

for the last value, the command start to stall.
Just a simple test. :)


>> how userland can be notified about throttling. Throttling could be
>> worth for operf too, not only for the oprofile kernel driver.
>>

>> From a quick look it seems there is also code in x86 that dynamically
>> adjusts the rate which might be worth being implemented for ARM too.
> 
> Are you referring to the perf_sample_event_took callback? If so, that
> certainly looks worth persuing. I'll stick it on my list, thanks!
> 

Thanks Will for doing this.

Thanks
Weng Meiling

> Will
> 
> .
> 



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