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Date: Sun, 7 Aug 2016 16:06:18 +0530 From: Janani Ravichandran <janani.rvchndrn@...il.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Janani Ravichandran <janani.rvchndrn@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, riel@...riel.com, akpm@...ux-foundation.org, hannes@...pxchg.org, vdavydov@...tuozzo.com, mhocko@...e.com, vbabka@...e.cz, mgorman@...hsingularity.net, kirill.shutemov@...ux.intel.com, bywxiaobai@....com Subject: Re: [PATCH 1/2] mm: page_alloc.c: Add tracepoints for slowpath > On Aug 5, 2016, at 10:00 PM, Steven Rostedt <rostedt@...dmis.org> wrote: > >> > > You probably want to clear the trace here, or set function_graph here > first. Because the function graph starts writing to the buffer > immediately. > I did that, just didn’t include it here :) >> > > When threshold is set, the entry is not recorded, because it is only > showing the exit and the time it took in that function: > > 0) kswapd0-52 | + 54.141 us | } /* shrink_zone */ > > shrink_zone() took 54.141us. > > The reason it doesn't record the entry is because it would fill the > entire buffer, if the threshold is never hit. One can't predict the > time in a function when you first enter that function. Right! > >> > > You need your own interpreter here. Perhaps a module that either reads > the tracepoints directly and registers a function graph tracer itself. > The trace events and function tracers are plugable. You don't need to > use the tracing system to use them. Just hook into them directly. > > Things like the wakeup latency tracer does this. Look at > kernel/trace/trace_sched_wakeup.c for an example. It hooks into the > sched_wakeup and sched_switch tracepoints, and also has a way to use > function and function_graph tracing. > > I will look at that file. Thanks! > >> > > Great! And note, even if you add extra tracepoints, you can hook > directly into them too. Again, see the trace_sched_wakeup.c for > examples. Alright. Thanks for all the help! :) Janani. > > -- Steve
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