linux-kernel - Re: [PATCH 1/7] trace/events: Add gup trace events

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Message-ID: <565E3DBC.9070204@linaro.org>
Date:	Tue, 01 Dec 2015 16:39:24 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	akpm@...ux-foundation.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH 1/7] trace/events: Add gup trace events

On 12/1/2015 4:18 PM, Steven Rostedt wrote:
> On Tue, 01 Dec 2015 16:07:44 -0800
> "Shi, Yang" <yang.shi@...aro.org> wrote:
>
>> On 12/1/2015 3:56 PM, Steven Rostedt wrote:
>>> On Tue,  1 Dec 2015 15:06:11 -0800
>>> Yang Shi <yang.shi@...aro.org> wrote:
>>>
>>>> page-faults events record the invoke to handle_mm_fault, but the invoke
>>>> may come from do_page_fault or gup. In some use cases, the finer event count
>>>> mey be needed, so add trace events support for:
>>>>
>>>> __get_user_pages
>>>> __get_user_pages_fast
>>>> fixup_user_fault
>>>>
>>>> Signed-off-by: Yang Shi <yang.shi@...aro.org>
>>>> ---
>>>>    include/trace/events/gup.h | 77 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 77 insertions(+)
>>>>    create mode 100644 include/trace/events/gup.h
>>>>
>>>> diff --git a/include/trace/events/gup.h b/include/trace/events/gup.h
>>>> new file mode 100644
>>>> index 0000000..37d18f9
>>>> --- /dev/null
>>>> +++ b/include/trace/events/gup.h
>>>> @@ -0,0 +1,77 @@
>>>> +#undef TRACE_SYSTEM
>>>> +#define TRACE_SYSTEM gup
>>>> +
>>>> +#if !defined(_TRACE_GUP_H) || defined(TRACE_HEADER_MULTI_READ)
>>>> +#define _TRACE_GUP_H
>>>> +
>>>> +#include <linux/types.h>
>>>> +#include <linux/tracepoint.h>
>>>> +
>>>> +TRACE_EVENT(gup_fixup_user_fault,
>>>> +
>>>> +	TP_PROTO(struct task_struct *tsk, struct mm_struct *mm,
>>>> +			unsigned long address, unsigned int fault_flags),
>>>> +
>>>> +	TP_ARGS(tsk, mm, address, fault_flags),
>>>> +
>>>> +	TP_STRUCT__entry(
>>>> +		__array(	char,	comm,	TASK_COMM_LEN	)
>>>
>>> Why save the comm? The tracing infrastructure should keep track of that.
>>
>> The code is referred to kmem.h which has comm copied. If it is
>> unnecessary, it definitely could be removed.
>
> Sometimes comm isn't that reliable. But really, the only tracepoint
> that should record it is sched_switch, and sched_wakeup. With those
> two, the rest of the trace points should be fine.
>
>>
>>>
>>>> +		__field(	unsigned long,	address		)
>>>> +	),
>>>> +
>>>> +	TP_fast_assign(
>>>> +		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
>>>> +		__entry->address	= address;
>>>> +	),
>>>> +
>>>> +	TP_printk("comm=%s address=%lx", __entry->comm, __entry->address)
>>>> +);
>>>> +
>>>> +TRACE_EVENT(gup_get_user_pages,
>>>> +
>>>> +	TP_PROTO(struct task_struct *tsk, struct mm_struct *mm,
>>>> +			unsigned long start, unsigned long nr_pages,
>>>> +			unsigned int gup_flags, struct page **pages,
>>>> +			struct vm_area_struct **vmas, int *nonblocking),
>>>> +
>>>> +	TP_ARGS(tsk, mm, start, nr_pages, gup_flags, pages, vmas, nonblocking),
>>>
>>> Why so many arguments? Most are not used.
>>
>> My understanding to TP_ARGS may be not right. Doesn't it require all the
>> args defined by the function? If not, it could definitely be shrunk.
>> Just need keep the args used by TP_printk?
>
> It only needs what is used by TP_fast_assign().

Thanks, will fix them in V2.

Yang

>
> -- Steve
>

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