Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

Ingo Molnar
2013-11-27T11:52:54Z

* Adrian Hunter <adrian.hunter@intel.com> wrote:

> On 27/11/13 13:32, Ingo Molnar wrote:
> >
> > * Adrian Hunter <adrian.hunter@intel.com> wrote:
> >
> >> On 26/11/13 18:15, Ingo Molnar wrote:
> >>>
> >>> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> >>>
> >>>> The logic was not looking in the buildid cache for kcore
> >>>> if the host kernel buildid did not match the recorded
> >>>> kernel buildid.
> >>>
> >>> It would be nice to also include the specific failure mode in the
> >>> changelog: exactly how can users run into this. That will be more
> >>> useful to most people reading these changelogs than a more abstract
> >>> bug description.
> >>
> >> The preconditions for the problem are that kcore is in the buildid
> >> cache and that the running kernel has a different buildid e.g.
> >>
> >> $ perf buildid-list | grep kernel.kallsyms
> >> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
> >>
> >> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
> >> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
> >>
> >>
> >>
> >> Before the patch:
> >>
> >>
> >> $ perf script -v >out.txt
> >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> >> <SNIP>
> >> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
> >>
> >> perf script stopped
> >>
> >>
> >> After the patch:
> >>
> >>
> >> $ perf script -v >out.txt
> >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> >> <SNIP>
> >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
> >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
> >>
> >> perf script stopped
> >
> > So the result of the patch is that kernel symbols get
> > resolved/annotated correctly, as expected from the live kcore feature,
> > right?
>
> Yes but this is the non-live case i.e. the kernel has changed and we are
> looking at a special copy of kcore that we placed in the buildid cache
> (using "perf buildid-cache -v -k /proc/kcore") when the data was recorded.

Okay.

Thanks,

Ingo