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Fri, 26 Jun 2026 04:38:52 -0700 (PDT) Received: from fedora ([5.12.139.217]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-492690a1a85sm124466935e9.15.2026.06.26.04.38.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jun 2026 04:38:51 -0700 (PDT) From: Claudiu Zissulescu To: binutils@sourceware.org Cc: jemarch@gnu.org, simone_maione@yahoo.com Subject: [PATCH 2/4] gprofng: mark non-precise HW counter columns Date: Fri, 26 Jun 2026 14:33:20 +0300 Message-ID: <20260626113840.44715-3-claziss@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260626113840.44715-1-claziss@gmail.com> References: <20260626113840.44715-1-claziss@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-11.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, PROLO_LEO2, RCVD_IN_DNSWL_NONE, RCVD_IN_PBL, SPF_HELO_NONE, SPF_PASS, TXREP shortcircuit=no autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on sourceware.org X-BeenThere: binutils@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Binutils mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: binutils-bounces~patchwork=sourceware.org@sourceware.org Mark the column header of any non-precise HW counter metric with "(*)" and emit a single explanatory footnote below the column header block when at least one displayed metric is non-precise. Precise PEBS/IBS events (ABST_EXACT, ABST_EXACT_PEBS_PLUS1) are left unmarked. Also point the user at the "Precise events" section of -h output. gprofng/ * src/Metric.cc (Metric::set_name): Append "*" marker. * src/Print.cc (print_label): Emit a footnote explaining the "*" marker. * src/Hist_data.cc (Hist_data::print_label): Likewise. --- gprofng/src/Hist_data.cc | 27 +++++++++++++++++++++++++++ gprofng/src/Metric.cc | 16 +++++++++++++--- gprofng/src/Print.cc | 26 ++++++++++++++++++++++++++ 3 files changed, 66 insertions(+), 3 deletions(-) diff --git a/gprofng/src/Hist_data.cc b/gprofng/src/Hist_data.cc index 41e3edf3ae4..8818e84f215 100644 --- a/gprofng/src/Hist_data.cc +++ b/gprofng/src/Hist_data.cc @@ -863,6 +863,33 @@ Hist_data::print_label (FILE *out_file, Metric::HistMetric *hist_metric, sb1.toFileLn (out_file); sb2.toFileLn (out_file); sb3.toFileLn (out_file); + + /* Footnote for non-precise HW counters (marked with " (*)" by + Metric::set_name). Emit once if any visible metric uses such a + counter, so users understand source-line attribution may skid. + Mirrors the equivalent block in the free print_label() in Print.cc. */ + bool any_non_precise = false; + for (int i = 0; i < nmetrics && !any_non_precise; i++) + { + Metric *m = metrics->get (i); + if (!m->is_any_visible ()) + continue; + if (m->get_type () != Metric::HWCNTR) + continue; + Hwcentry *hwc = m->get_hw_ctr (); + if (hwc != NULL + && !HWCENTRY_USES_SAMPLING (hwc) + && hwc->memop != ABST_EXACT) + any_non_precise = true; + } + if (any_non_precise) + fprintf (out_file, GTXT ( + "%*s(*) Non-precise HW event: sample location may skid forward by\n" + "%*s several instructions, so cache/branch misses are often\n" + "%*s attributed to the next basic block (e.g. a loop header).\n" + "%*s For exact line attribution, prefer precise events\n" + "%*s (see the \"Precise events\" section of `gprofng collect app -h`).\n"), + space, "", space, "", space, "", space, "", space, ""); return name_offset; } diff --git a/gprofng/src/Metric.cc b/gprofng/src/Metric.cc index a72bdaef6a3..f4264277bf9 100644 --- a/gprofng/src/Metric.cc +++ b/gprofng/src/Metric.cc @@ -306,7 +306,8 @@ Metric::set_subtype (SubType st) case HWCNTR: { char *sstr, *estr1, *estr2; - if (get_hw_ctr () == NULL) + Hwcentry *hwc = get_hw_ctr (); + if (hwc == NULL) abort (); sstr = get_username (); if (st == EXCLUSIVE) @@ -335,8 +336,17 @@ Metric::set_subtype (SubType st) get_aux (), st); estr2 = dbe_strdup (NTXT ("??")); } - name = dbe_sprintf (NTXT ("%s%s"), estr1, sstr); - abbr = dbe_sprintf (NTXT ("%s%s"), estr2, sstr); + /* Mark non-precise counters so users don't over-trust source-line + attribution. Only PEBS/EXACT events tag the retiring instruction; + everything else may skid forward by several instructions. The (*) + should be explained by a footnote at report-print time. */ + const char *mark = ""; + if ((st == EXCLUSIVE || st == INCLUSIVE || st == DATASPACE) + && !HWCENTRY_USES_SAMPLING (hwc) + && hwc->memop != ABST_EXACT) + mark = " (*)"; + name = dbe_sprintf (NTXT ("%s%s%s"), estr1, sstr, mark); + abbr = dbe_sprintf (NTXT ("%s%s%s"), estr2, sstr, mark); break; } diff --git a/gprofng/src/Print.cc b/gprofng/src/Print.cc index 564e3a638bc..8d3cef4ede4 100644 --- a/gprofng/src/Print.cc +++ b/gprofng/src/Print.cc @@ -306,6 +306,32 @@ print_label (FILE *out_file, MetricList *metrics_list, fprintf (out_file, NTXT ("%*s%s\n"), space, NTXT (""), delTrailingBlanks (line1)); fprintf (out_file, NTXT ("%*s%s\n"), space, NTXT (""), delTrailingBlanks (line2)); fprintf (out_file, NTXT ("%*s%s\n"), space, NTXT (""), delTrailingBlanks (line3)); + + /* Footnote for non-precise HW counters (marked with " (*)" by + Metric::set_name). Emit once if any visible metric uses such a + counter, so users understand source-line attribution may skid. */ + bool any_non_precise = false; + for (int i = 0, n = mlist->size (); i < n && !any_non_precise; i++) + { + Metric *m = mlist->fetch (i); + if (!(m->is_visible () || m->is_tvisible () || m->is_pvisible ())) + continue; + if (m->get_type () != Metric::HWCNTR) + continue; + Hwcentry *hwc = m->get_hw_ctr (); + if (hwc != NULL + && !HWCENTRY_USES_SAMPLING (hwc) + && hwc->memop != ABST_EXACT) + any_non_precise = true; + } + if (any_non_precise) + fprintf (out_file, GTXT ( + "%*s(*) Non-precise HW event: sample location may skid forward by\n" + "%*s several instructions, so cache/branch misses are often\n" + "%*s attributed to the next basic block (e.g. a loop header).\n" + "%*s For exact line attribution, prefer precise events\n" + "%*s (see the \"Precise events\" section of `gprofng collect app -h`).\n"), + space, "", space, "", space, "", space, "", space, ""); return name_offset; }