linux-kernel - Re: [PATCH v2 0/7] perf trace pagefaults

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Date:	Mon, 23 Jun 2014 08:00:31 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Stanislav Fomichev <stfomichev@...dex-team.ru>
CC:	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	jolsa@...hat.com, xiaoguangrong@...ux.vnet.ibm.com,
	yangds.fnst@...fujitsu.com, adrian.hunter@...el.com,
	namhyung@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/7] perf trace pagefaults

On 6/20/14, 9:24 AM, Arnaldo Carvalho de Melo wrote:
> Right now it is too simple, but I was starting to work (when you jumped
> right in with your work making me stop and go on testing/reviewing :) )
> on making it more generic so that we could defer pretty printing the
> arguments from sys_enter to sys_exit, when, by then, we would already
> have an association of a user level pointer in some specific thread to
> its contents.
>
> This will allow us to to resolve the pathname pointer in things like
> open() (i.e. not just after that, in the fd syscalls (write, etc)) and
> as well any other pointer of interest.
>
> By librarizing 'builtin-probe.c', that now uses lots of global
> variables, etc, we would be able to insert probes where we want them to
> capture the contents of pointers, check if the probes are already in
> place, use just the ones that we managed to insert (i.e. that were not
> invalid because the places where we wanted them to be were changed
> across kernel releases, etc).
>
> I.e. no need for actual tracepoints from day one, just wannabe
> tracepoints using whatever probe inserting gizmo the kprobes_tracer used
> by 'perf probe' now thinks its best to use.
>
> Combine that with using DWARF descriptions (that could be pre cached
> into something like CTF (the DTrace kind of CTF) or similar) like pahole
> does and we would mostly automatically do all this work of prettyfing
> syscall parameters.
>
> </handwave>

That was so much handwaving you could keep cool at a World Cup game. :-)

David

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