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Date: Sat, 16 Oct 2010 02:19:02 +0200 From: Frederic Weisbecker <fweisbec@...il.com> To: Peter Zijlstra <peterz@...radead.org> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>, Arnaldo Carvalho de Melo <acme@...hat.com>, Paul Mackerras <paulus@...ba.org>, Stephane Eranian <eranian@...gle.com>, Cyrill Gorcunov <gorcunov@...nvz.org>, Tom Zanussi <tzanussi@...il.com>, Masami Hiramatsu <mhiramat@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Robert Richter <robert.richter@....com> Subject: Re: [RFC PATCH 4/9] perf: Don't record frame pointer based user stacktraces if we dump stack and regs On Wed, Oct 13, 2010 at 09:23:06AM +0200, Peter Zijlstra wrote: > On Wed, 2010-10-13 at 07:06 +0200, Frederic Weisbecker wrote: > > User and kernel stack might be selected for other uses than callchain > > in the future, this probably shouldn't mess with the regular callchain > > code. Instead we should probably have an exclude_callchain_user > > attribute, that could be also useful to filter out user callchains > > when people don't want them. > > Probably ;-) There is another solution that would solve my vdso problem in the meantime. The problem with vdso is that if we entered the kernel with a syscall, the first user entry in the callchain will be a vdso address. But vdso doesn't have dwarf informations so we can't unwind further. One solution would be having max_callchain_user as an attribute. If we do a normal frame pointer based callchain, set it to -1 and you won't have limitations in your callchain. Or you can set it to n so that your callchains are bound to a maximum depth. If you don't want user callchains, set it to 0. If you do a dwarf based callchain, set it to 2, so that if userspace was in a vdso, we just deref the frame pointer to find what called the vdso, and then we can start the dwarf unwinding from there. I think I'll try that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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