From: Steven Rostedt <rostedt@goodmis.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Janani Ravichandran <janani.rvchndrn@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
riel@surriel.com, akpm@linux-foundation.org, hannes@compxchg.org,
vdavydov@virtuozzo.com, mhocko@suse.com, vbabka@suse.cz,
mgorman@techsingularity.net, kirill.shutemov@linux.intel.com,
bywxiaobai@163.com
Subject: Re: [PATCH 1/2] mm: page_alloc.c: Add tracepoints for slowpath
Date: Wed, 27 Jul 2016 13:30:08 -0400 [thread overview]
Message-ID: <20160727133008.74e52024@gandalf.local.home> (raw)
In-Reply-To: <5798ED5C.1020300@intel.com>
On Wed, 27 Jul 2016 10:20:28 -0700
Dave Hansen <dave.hansen@intel.com> wrote:
> On 07/27/2016 08:23 AM, Steven Rostedt wrote:
> >> > +
> >> > + trace_mm_slowpath_end(page);
> >> > +
> > I'm thinking you only need one tracepoint, and use function_graph
> > tracer for the length of the function call.
> >
> > # cd /sys/kernel/debug/tracing
> > # echo __alloc_pages_nodemask > set_ftrace_filter
> > # echo function_graph > current_tracer
> > # echo 1 > events/kmem/trace_mm_slowpath/enable
>
> I hesitate to endorse using the function_graph tracer for this kind of
> stuff. Tracepoints offer some level of stability in naming, and the
> compiler won't ever make them go away. While __alloc_pages_nodemask is
> probably more stable than most things, there's no guarantee that it will
> be there.
Well, then you are also advocating in a userspace ABI interface that
will have to be maintained forever. Just be warned.
>
> BTW, what's the overhead of the function graph tracer if the filter is
> set up to be really restrictive like above? Is the overhead really just
> limited to that one function?
Yes, if DYNAMIC_FTRACE is defined. Which it should be, because static
ftrace has a huge overhead without enabling the tracer.
It will enable only that function to be traced. I've recommend before
that if one wants to have a good idea of how long a function lasts,
they should filter to a single function. Anything else will include
overhead of the tracer itself.
-- Steve
next prev parent reply other threads:[~2016-07-27 17:30 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-27 14:43 [PATCH 0/2] New tracepoints for slowpath and memory compaction Janani Ravichandran
2016-07-27 14:47 ` [PATCH 1/2] mm: page_alloc.c: Add tracepoints for slowpath Janani Ravichandran
2016-07-27 15:23 ` Steven Rostedt
2016-07-27 17:20 ` Dave Hansen
2016-07-27 17:30 ` Steven Rostedt [this message]
2016-07-28 20:11 ` Janani Ravichandran
2016-08-04 15:19 ` Steven Rostedt
2016-08-05 16:03 ` Janani Ravichandran
2016-08-05 16:30 ` Steven Rostedt
2016-08-07 10:36 ` Janani Ravichandran
2016-07-27 16:33 ` Michal Hocko
2016-07-27 18:16 ` Rik van Riel
2016-07-27 18:28 ` Steven Rostedt
2016-07-27 18:44 ` Michal Hocko
2016-07-27 18:57 ` Rik van Riel
2016-07-27 14:51 ` [PATCH 2/2] mm: compaction.c: Add/Modify direct compaction tracepoints Janani Ravichandran
2016-07-27 15:24 ` Steven Rostedt
2016-08-01 13:25 ` Vlastimil Babka
2016-08-07 12:32 ` Janani Ravichandran
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