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

[Shi, Yang]

On 12/1/2015 4:18 PM, Steven Rostedt wrote:
> On Tue, 01 Dec 2015 16:07:44 -0800
> "Shi, Yang" <yang.shi@xxxxxxxxxx> wrote:
>
> > On 12/1/2015 3:56 PM, Steven Rostedt wrote:
> > > On Tue,  1 Dec 2015 15:06:11 -0800
> > > Yang Shi <yang.shi@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > ---
> > > >    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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