linux-kernel - Re: [PATCH V2 1/7] trace/events: Add gup trace events

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Message-ID: <20151202230758.0411d8c9@grimm.local.home>
Date:	Wed, 2 Dec 2015 23:07:58 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yang Shi <yang.shi@...aro.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 V2 1/7] trace/events: Add gup trace events

On Wed,  2 Dec 2015 14:53:27 -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 | 71 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 71 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..03a4674
> --- /dev/null
> +++ b/include/trace/events/gup.h
> @@ -0,0 +1,71 @@
> +#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),

Arges added and not used by TP_fast_assign(), this will slow down the
code while tracing is enabled, as they need to be added to the trace
function call.

> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned long,	address		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->address	= address;
> +	),
> +
> +	TP_printk("address=%lx",  __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),
> +
> +	TP_ARGS(tsk, mm, start, nr_pages),

Here too but this is worse. See below.

> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned long,	start		)
> +		__field(	unsigned long,	nr_pages	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->start		= start;
> +		__entry->nr_pages	= nr_pages;
> +	),
> +
> +	TP_printk("start=%lx nr_pages=%lu", __entry->start, __entry->nr_pages)
> +);
> +
> +TRACE_EVENT(gup_get_user_pages_fast,
> +
> +	TP_PROTO(unsigned long start, int nr_pages, int write,
> +			struct page **pages),
> +
> +	TP_ARGS(start, nr_pages, write, pages),

This and the above "gup_get_user_pages" have the same entry field,
assign and printk. They should be combined into a DECLARE_EVENT_CLASS()
and two DEFINE_EVENT()s. That will save on size as the
DECLARE_EVENT_CLASS() is the biggest part of each TRACE_EVENT().

-- Steve


> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned long,	start		)
> +		__field(	unsigned long,	nr_pages	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->start  	= start;
> +		__entry->nr_pages	= nr_pages;
> +	),
> +
> +	TP_printk("start=%lx nr_pages=%lu",  __entry->start, __entry->nr_pages)
> +);
> +
> +#endif /* _TRACE_GUP_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>

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