linux-kernel - Re: [PATCH v3 3/7] perf tools: Remove the logical that skip buildid cache if symfs is given

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Date:	Fri, 13 May 2016 15:01:04 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Hekuang <hekuang@...wei.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	peterz@...radead.org, mingo@...hat.com,
	alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
	wangnan0@...wei.com, jpoimboe@...hat.com, ak@...ux.intel.com,
	eranian@...gle.com, namhyung@...nel.org, adrian.hunter@...el.com,
	sukadev@...ux.vnet.ibm.com, masami.hiramatsu.pt@...achi.com,
	tumanova@...ux.vnet.ibm.com, kan.liang@...el.com,
	penberg@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/7] perf tools: Remove the logical that skip buildid
 cache if symfs is given

Em Fri, May 13, 2016 at 08:27:29AM -0600, David Ahern escreveu:
> On 5/13/16 1:19 AM, Hekuang wrote:
> > > What about putting the build id cache under the symfs? so instead of
> > > dropping the symfs check and it to the path for the build id cache.

> > I think your intention is to reference symbol files in one place
> > instead of two. So there're two possible approaches, one is all
> > in buildid-cache, but in practice, I found lots of binaries in
> > symfs even not contains valid buildid, so this way is not work.

> > The other one is all in symfs. It seems ok, but one problem I
> > should point out, with my test environment as an example, the
> > symfsdir is $(TARGET_ROOTFS),and by default buildid_dir is
> > $(TARGET_ROOTFS)/$(HOME)/.debug/, host perf does not know
> > $(HOME) folder in target and we should copy the debug folder
> >  to $(TARGET_ROOTFS), which is readonly in the target. For me, it's
> > easier to use 'buildid-cache -a vdso-xxxx' to add that into host
> > buildid-cache than copy debug folder from $(HOME) to readonly
> > $(TARGET_ROOTFS).

> > Without the stale concern, I prefer the two places(buildid-dir in
> > host and target symfs) way.
> 
> The intention of symfs is every single file opened by perf is relative to
> that directory. As I recall when I added that option in early 2011 I made
> sure that statement is true. I think it is best to maintain that design.

Ok, so we can introduce --dso-prefix for Hekuang's use case, i.e. be able
to lookup by build-id, fallbacking to a (possibly read-only) directory.

This way the existing --symfs semantic remains written in stone.

- Arnaldo