Messages in this thread | | | Date | Tue, 29 Mar 2022 16:16:11 +0200 | From | "Steinar H. Gunderson" <> | Subject | Re: [PATCH] perf intel-pt: Synthesize cycle events |
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On Tue, Mar 29, 2022 at 02:31:14PM +0200, Steinar H. Gunderson wrote: > int64_t _sort__sym_cmp(struct symbol *sym_l, struct symbol *sym_r) > { > if (!sym_l || !sym_r) > return cmp_null(sym_l, sym_r); > > if (sym_l == sym_r) > return 0; > > if (sym_l->inlined || sym_r->inlined) { > int ret = strcmp(sym_l->name, sym_r->name); > > if (ret) > return ret; > if ((sym_l->start <= sym_r->end) && (sym_l->end >= sym_r->start)) > return 0; > } > > if (sym_l->start != sym_r->start) > return (int64_t)(sym_r->start - sym_l->start);
Even fixing <= to <, I do get nonsensical results like an inlined (and very small) destructor taking 50%+ of CPU time, and having a huge call chain under it. It largely goes away (I'm not sure if it's perfect) if I remove the entire if (sym_l->inlined || ... branch, but I guess it's there for a reason.
Thinking about it, I wonder if this code breaks the entire tree invariant of comparison being transitive. If left _or_ right is inlined, it compares them by name, but if not, it compares them by address. So you can have three symbols A, B (inline) and C, where A < B (on name), B < C (on name) but C < A (on address; assuming C has a lower start address than A). That doesn't look good to me.
I'm wondering if the right fix would be something like replacing the entire if with something like
if (sym_l->inlined && sym_r->inlined && strcmp(sym_l->name, sym_r->name) == 0) && <keep [start,end) overlap test here>) { return 0; }
but I'm not sure.
/* Steinar */
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