linux-kernel - Re: [PATCH V2 2/7] mm/gup: add gup trace points

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Date:	Wed, 02 Dec 2015 16:52:26 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Dave Hansen <dave.hansen@...el.com>, akpm@...ux-foundation.org,
	rostedt@...dmis.org, mingo@...hat.com
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH V2 2/7] mm/gup: add gup trace points

On 12/2/2015 4:11 PM, Shi, Yang wrote:
> On 12/2/2015 3:36 PM, Dave Hansen wrote:
>> On 12/02/2015 02:53 PM, Yang Shi wrote:
>>> diff --git a/mm/gup.c b/mm/gup.c
>>> index deafa2c..10245a4 100644
>>> --- a/mm/gup.c
>>> +++ b/mm/gup.c
>>> @@ -13,6 +13,9 @@
>>>   #include <linux/rwsem.h>
>>>   #include <linux/hugetlb.h>
>>>
>>> +#define CREATE_TRACE_POINTS
>>> +#include <trace/events/gup.h>
>>> +
>>>   #include <asm/pgtable.h>
>>>   #include <asm/tlbflush.h>
>>
>> This needs to be _the_ last thing that gets #included.  Otherwise, you
>> risk colliding with any other trace header that gets implicitly included
>> below.
>
> Thanks for the suggestion, will move it to the last.
>
>>
>>> @@ -1340,6 +1346,8 @@ int __get_user_pages_fast(unsigned long start,
>>> int nr_pages, int write,
>>>                       start, len)))
>>>           return 0;
>>>
>>> +    trace_gup_get_user_pages_fast(start, nr_pages, write, pages);
>>> +
>>>       /*
>>>        * Disable interrupts.  We use the nested form as we can
>>> already have
>>>        * interrupts disabled by get_futex_key.
>>
>> It would be _really_ nice to be able to see return values from the
>> various gup calls as well.  Is that feasible?
>
> I think it should be feasible. kmem_cache_alloc trace event could show
> return value. I'm supposed gup trace events should be able to do the
> same thing.

Just did a quick test, it is definitely feasible. Please check the below 
test log:

        trace-cmd-200   [000]    99.221486: gup_get_user_pages: 
start=8000000ff0 nr_pages=1 ret=1
        trace-cmd-200   [000]    99.223215: gup_get_user_pages: 
start=8000000fdb nr_pages=1 ret=1
        trace-cmd-200   [000]    99.223298: gup_get_user_pages: 
start=8000000ed0 nr_pages=1 ret=1

nr_pages is the number of pages requested by the gup, ret is the return 
value.

If nobody has objection, I will add it into V3.

Regards,
Yang

>
> Regards,
> Yang
>
>>
>

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