linux-kernel - Re: [PATCH 0/2] perf probe fixes for ppc64le

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Message-ID: <20160411134325.GM15993@naverao1-tp.in.ibm.com>
Date:	Mon, 11 Apr 2016 19:13:26 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Michael Ellerman <mpe@...erman.id.au>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Balbir Singh <bsingharora@...il.com>, linux-kernel@...r.kernel.org,
	Mark Wielaard <mjw@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [PATCH 0/2] perf probe fixes for ppc64le

On 2016/04/11 02:41PM, Michael Ellerman wrote:
> On Sat, 2016-04-09 at 19:12 +0530, Naveen N. Rao wrote:
> > 
> > I suppose this boils down to the quirkiness of ABIv2. Though, in 
> > reality, I don't think most users will notice. As I stated above, users 
> > will most likely start with the disassembly or debuginfo and this patch 
> > ensures there are actually no surprises there.
> 
> Yeah it's unfortunate that we have to handle these two cases differently.
> 
> But I think you've chosen the right trade off.
> 
> When we are just given the name we *must not* use the global entry point,
> otherwise the probes will often not hit - because most calls go to the local
> entry point and skip the global entry point entirely.
> 
> When we're given a name and offset, it's less confusing if we use the global
> entry point as the base for the offset calculation.
> 
> So for the concept:
> 
> Acked-by: Michael Ellerman <mpe@...erman.id.au>

Thanks, Michael. That helps.

> 
> I don't really know this part of the perf code enough to give you an ack for the
> actual changes, I'll leave that to the perf maintainers.

Sure.

Arnaldo,
I will send a v2 soon with a bit more testing to make sure this covers 
all scenarios properly (I am also trying to see if we can address 
debuginfo-based probing properly).

- Naveen