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

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Date:	Tue, 24 Jun 2014 11:15:01 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Stanislav Fomichev <stfomichev@...dex-team.ru>
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org,
	Ingo Molnar <mingo@...nel.org>, dsahern@...il.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

Em Mon, Jun 23, 2014 at 03:41:39PM +0400, Stanislav Fomichev escreveu:
> > > But we then need to predefine many probes for decoding to work in the form of
> > > func:offset, and then play catch-up with all the kernel changes.
> > > Or I miss something important here?

> > No you don't.

> > If we want to disturb the system in the least way possible, we need to
> > tag along the copying from userspace of those pointers, so that we get
> > them fresh and just stash it in our ring buffer and get out of the way
> > quickly.

> I just thought maybe you have some grand plan in mind about automagically
> adding probes so argument tracing works transparently. I like the
> approach though.

First we use what we have in place, then we optimize it.
 
> > Almost a year ago, and it still works, now lets see the cset you mention...
> > 
> > [acme@zoo linux]$ git describe c4ad8f98bef77c7356aa6a9ad9188a6acc6b849d
> > v3.14-rc1-14-gc4ad8f98bef7
> > [acme@zoo linux]$
> > [root@zoo ~]# uname -r
> > 3.15.0-rc8+
> > 
> > Humm, what is the problem?

> I thought that result->name was actually set on 65th line of
> getname_flags, so the above commit would move it to 66th. But it's not
> the case, sorry for confusion.
 
> > [1] And I feel like all of tools/perf/ is just that, reference implementations, but hopefully
> >     done in a such a way that may well be useful as-is :-)

> I'd like perf to be a goto tool for all kind of performance analysis,

yay, and you're working for that, thanks!

> not just a reference implementation. I believe nobody looks at this
> reference, and we end up with tools like https://github.com/draios/sysdig

Never heard about it, will take a look, thanks for the pointer.

> which do their own events, ring buffer, etc.

There are several out there :)

- Arnaldo
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