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Subject[PATCH 4.8 031/140] perf intel-pt: Fix MTC timestamp calculation for large MTC periods
Date
4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Adrian Hunter <adrian.hunter@intel.com>

commit 3bccbe20f6d188ce7b00326e776b745cfd35b10a upstream.

The MTC packet provides a 8-bit slice of CTC which is related to TSC by
the TMA packet, however the TMA packet only provides the lower 16 bits
of CTC. If mtc_shift > 8 then some of the MTC bits are not in the CTC
provided by the TMA packet. Fix-up the last_mtc calculated from the TMA
packet by copying the missing bits from the current MTC assuming the
least difference between the two, and that the current MTC comes after
last_mtc.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1475062896-22274-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/perf/util/intel-pt-decoder/intel-pt-decoder.c | 36 ++++++++++++++++++++
1 file changed, 36 insertions(+)

--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -89,6 +89,7 @@ struct intel_pt_decoder {
bool pge;
bool have_tma;
bool have_cyc;
+ bool fixup_last_mtc;
uint64_t pos;
uint64_t last_ip;
uint64_t ip;
@@ -584,10 +585,31 @@ struct intel_pt_calc_cyc_to_tsc_info {
uint64_t tsc_timestamp;
uint64_t timestamp;
bool have_tma;
+ bool fixup_last_mtc;
bool from_mtc;
double cbr_cyc_to_tsc;
};

+/*
+ * MTC provides a 8-bit slice of CTC but the TMA packet only provides the lower
+ * 16 bits of CTC. If mtc_shift > 8 then some of the MTC bits are not in the CTC
+ * provided by the TMA packet. Fix-up the last_mtc calculated from the TMA
+ * packet by copying the missing bits from the current MTC assuming the least
+ * difference between the two, and that the current MTC comes after last_mtc.
+ */
+static void intel_pt_fixup_last_mtc(uint32_t mtc, int mtc_shift,
+ uint32_t *last_mtc)
+{
+ uint32_t first_missing_bit = 1U << (16 - mtc_shift);
+ uint32_t mask = ~(first_missing_bit - 1);
+
+ *last_mtc |= mtc & mask;
+ if (*last_mtc >= mtc) {
+ *last_mtc -= first_missing_bit;
+ *last_mtc &= 0xff;
+ }
+}
+
static int intel_pt_calc_cyc_cb(struct intel_pt_pkt_info *pkt_info)
{
struct intel_pt_decoder *decoder = pkt_info->decoder;
@@ -617,6 +639,11 @@ static int intel_pt_calc_cyc_cb(struct i
return 0;

mtc = pkt_info->packet.payload;
+ if (decoder->mtc_shift > 8 && data->fixup_last_mtc) {
+ data->fixup_last_mtc = false;
+ intel_pt_fixup_last_mtc(mtc, decoder->mtc_shift,
+ &data->last_mtc);
+ }
if (mtc > data->last_mtc)
mtc_delta = mtc - data->last_mtc;
else
@@ -685,6 +712,7 @@ static int intel_pt_calc_cyc_cb(struct i

data->ctc_delta = 0;
data->have_tma = true;
+ data->fixup_last_mtc = true;

return 0;

@@ -751,6 +779,7 @@ static void intel_pt_calc_cyc_to_tsc(str
.tsc_timestamp = decoder->tsc_timestamp,
.timestamp = decoder->timestamp,
.have_tma = decoder->have_tma,
+ .fixup_last_mtc = decoder->fixup_last_mtc,
.from_mtc = from_mtc,
.cbr_cyc_to_tsc = 0,
};
@@ -1241,6 +1270,7 @@ static void intel_pt_calc_tma(struct int
}
decoder->ctc_delta = 0;
decoder->have_tma = true;
+ decoder->fixup_last_mtc = true;
intel_pt_log("CTC timestamp " x64_fmt " last MTC %#x CTC rem %#x\n",
decoder->ctc_timestamp, decoder->last_mtc, ctc_rem);
}
@@ -1255,6 +1285,12 @@ static void intel_pt_calc_mtc_timestamp(

mtc = decoder->packet.payload;

+ if (decoder->mtc_shift > 8 && decoder->fixup_last_mtc) {
+ decoder->fixup_last_mtc = false;
+ intel_pt_fixup_last_mtc(mtc, decoder->mtc_shift,
+ &decoder->last_mtc);
+ }
+
if (mtc > decoder->last_mtc)
mtc_delta = mtc - decoder->last_mtc;
else

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