Re: [PATCH V6 17/17] perf tools: choose to dump callchain from LBR and FP

Jiri Olsa
2014-10-24T13:55:27Z

On Fri, Oct 24, 2014 at 03:36:00PM +0200, Jiri Olsa wrote:
> On Sun, Oct 19, 2014 at 05:55:12PM -0400, Kan Liang wrote:
>
> SNIP
>
> > - return 0;
> > - }
> > - continue;
> > + mix_chain_nr = i + 2 + lbr_nr;
> > + if (mix_chain_nr > PERF_MAX_STACK_DEPTH) {
> > + pr_warning("corrupted callchain. skipping...\n");
> > + return 0;
> > }
> >
> > - al.filtered = 0;
> > - thread__find_addr_location(thread, machine, cpumode,
> > - MAP__FUNCTION, ip, &al);
> > - if (al.sym != NULL) {
> > - if (sort__has_parent && !*parent &&
> > - symbol__match_regex(al.sym, &parent_regex))
> > - *parent = al.sym;
> > - else if (have_ignore_callees && root_al &&
> > - symbol__match_regex(al.sym, &ignore_callees_regex)) {
> > - /* Treat this symbol as the root,
> > - forgetting its callees. */
> > - *root_al = al;
> > - callchain_cursor_reset(&callchain_cursor);
> > + for (j = 0; j < mix_chain_nr; j++) {
> > + struct addr_location al;
> > +
> > + if (callchain_param.order == ORDER_CALLEE) {
> > + if (j < i + 2)
> > + ip = chain->ips[j];
> > + else
> > + ip = lbr_stack->entries[j - i - 2].from;
> > + } else {
> > + if (j < lbr_nr)
> > + ip = lbr_stack->entries[lbr_nr - j - 1].from;
> > + else
> > + ip = chain->ips[i + 1 - (j - lbr_nr)];
> > }
> > + err = __machine__resolve_callchain_sample(machine,
> > + thread, ip, &cpumode, parent, root_al, &al);
> > + /* Discard all when the callchain is corrupted */
> > + if (err > 0)
> > + return 0;
> > + else if (err)
> > + return err;
>
> so you print FP callchains followed by LBR stack data, right?
>
> but AFAICS from kernel changes the FP callchains and LBR callchains
> data are unrelated.. 2 datasources of the same information
>
> do we rather want to print them separately? or using an option
> as Andi did in his lbr-as-callgraph patchset:
> http://marc.info/?l=linux-kernel&m=141177467802602&w=2

hum, sorry I've got confused by perf report -D output:

5719019682019 0x2128 [0x80]: PERF_RECORD_SAMPLE(IP, 0x2): 2499/2499: 0x401791 period: 327077 addr: 0
... chain: nr:3
..... 0: fffffffffffffe00 FP
..... 1: 0000000000401791 FP
..... 2: 00000032dca21d63 LBR
..... 3: 000000000040184c LBR

which sometimes displays user space FP data with LBR.. but I guess
the intention was to display either userspace FP or LBR, right?

I think we should have an option to be able to choose/switch.
Once general option that will tell report to use:
FP, DWARF, LBR (branches), LBR (callchain)

setting by default whatever the best option is based on the data we have.

thanks,
jirka