This series implements a solution for measuring the latency of
XSAVES/XRSTORS instructions on x86 processors. The motivation for This
solution is to provide a way to identify potential bottlenecks and
anomalies in the implementation of these instructions on different X86
hardware platforms and identify when the cost of XSAVES/XRSTORS is
increasing or decreasing. And Get the RFBM and XINUSE to figure out reason
if there are any issues.
The solution enables the comparison of the latency of the FPU across
different systems from various vendors over an long period of time.
The solution consists of two parts:
1. Two new tracepoints that calculate delta TSC as the latency.
2. A user-space tool that consumes trace logs and shows results.
We conducted extensive internal testing and compared several latency
computation methodologies. We believe it could be improved. Also the script
for consuming trace logs uses sqlite3 to display statistics data such as
max and min latency, and 97% tail latency, etc.
- Change from v6 to v7:
- Rebase patch to the most recent tag v6.6-rc1, no conflict.
- Remove all the additional crusts when disable CONFIG_X86_DEBUG_FPU.
(Ingo Molnar)
- Change from v5 to v6:
- Rebase patch to the most recent tag v6.5-rc7, no conflict.
- Add a colomn 'count' to the output of the script.
- Change from v4 to v5:
- Rebase patch to the most recent tag v6.1-rc2, no conflict.
- Change from v3 to v4:
- Rebase patch set to the latest tag v6.0-rc3, replacing
ALTERNATIVE_2 with ALTERNATIVE_3
- Change from v2 to v3:
- Move the script xsave-latency-trace.sh to folder tools/testing/fpu/
(Ingo Molnar)
- Change from v1 to v2:
- Reword the comments. (Laight, David; Mehta, Sohil)
- Rename all variable 'dtsc' to 'latency'. (Mehta, Sohil)
*** BLURB HERE ***
Yi Sun (3):
x86/fpu: Measure the Latency of XSAVE and XRSTOR
tools/testing/fpu: Add script to consume trace log of xsave latency
tools/testing/fpu: Add a 'count' column.
arch/x86/include/asm/trace/fpu.h | 37 ++++
arch/x86/kernel/fpu/xstate.h | 42 +++-
tools/testing/fpu/xsave-latency-trace.sh | 234 +++++++++++++++++++++++
3 files changed, 308 insertions(+), 5 deletions(-)
create mode 100755 tools/testing/fpu/xsave-latency-trace.sh
--
2.34.1
From d9f24eb83ef259ccea780caee02abdd2db5911b5 Mon Sep 17 00:00:00 2001
From: Yi Sun <[email protected]>
Date: Fri, 1 Sep 2023 20:05:01 +0800
Yi Sun (3):
x86/fpu: Measure the Latency of XSAVE and XRSTOR
tools/testing/fpu: Add script to consume trace log of xsave latency
tools/testing/fpu: Add a 'count' column.
arch/x86/include/asm/trace/fpu.h | 35 ++++
arch/x86/kernel/fpu/xstate.h | 49 ++++-
tools/testing/fpu/xsave-latency-trace.sh | 234 +++++++++++++++++++++++
3 files changed, 313 insertions(+), 5 deletions(-)
create mode 100755 tools/testing/fpu/xsave-latency-trace.sh
--
2.34.1
Add two trace points x86_fpu_latency_xsave and x86_fpu_latency_xrstor.
The latency dumped by the new trace points can tell when XSAVE/XRSTOR
are getting more or less expensive, and get out the RFBM
(requested-feature bitmap) and XINUSE to figure out the reason.
Calculate the latency of instructions XSAVE and XRSTOR within a
single trace event respectively. Another option considered was to
have 2 separated trace events marking the start and finish of the
XSAVE/XRSTOR. The latency was calculated from the 2 trace points in
user space, but there was significant overhead added by the trace
function itself.
In internal testing, the single trace point option which is
implemented here proved to save big overhead introduced by trace
function.
Make use of trace_clock() to calculate the latency, which is based on
cpu_clock() with precision at most ~1 jiffy between CPUs.
Configure CONFIG_X86_DEBUG_FPU is required. And the compiler will get
rid of all the extra crust when CONFIG_X86_DEBUG_FPU is disabled.
If both of the configs are enabled, the function tracepoint_enabled
would be reduced to a static check for tracing enabled. Thus, in the
fast path there would be only 2 additional static checks.
Since trace points can be enabled dynamically, while the code is
checking tracepoint_enabled(trace_event), the trace_event could be
concurrently enabled. Hence there is probability to get single once
noisy result 'trace_clock() - (-1)' at the moment enabling the trace
points x86_fpu_latency_*. Leave the noise here instead of additional
conditions while calling the x86_fpu_latency_* because it's not worth
for the only once noise. It's easy to filter out by the following
consuming script or other user space tool.
Trace log looks like following:
x86_fpu_latency_xsave: x86/fpu: latency:100 RFBM:0x202e7 XINUSE:0x202
x86_fpu_latency_xrstor: x86/fpu: latency:99 RFBM:0x202e7 XINUSE:0x202
Reviewed-by: Sohil Mehta <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
Signed-off-by: Yi Sun <[email protected]>
diff --git a/arch/x86/include/asm/trace/fpu.h b/arch/x86/include/asm/trace/fpu.h
index 4645a6334063..0640fe79edf3 100644
--- a/arch/x86/include/asm/trace/fpu.h
+++ b/arch/x86/include/asm/trace/fpu.h
@@ -89,6 +89,43 @@ DEFINE_EVENT(x86_fpu, x86_fpu_xstate_check_failed,
TP_ARGS(fpu)
);
+#if defined(CONFIG_X86_DEBUG_FPU)
+DECLARE_EVENT_CLASS(x86_fpu_latency,
+ TP_PROTO(struct fpstate *fpstate, u64 latency),
+ TP_ARGS(fpstate, latency),
+
+ TP_STRUCT__entry(
+ __field(struct fpstate *, fpstate)
+ __field(u64, latency)
+ __field(u64, rfbm)
+ __field(u64, xinuse)
+ ),
+
+ TP_fast_assign(
+ __entry->fpstate = fpstate;
+ __entry->latency = latency;
+ __entry->rfbm = fpstate->xfeatures;
+ __entry->xinuse = fpstate->regs.xsave.header.xfeatures;
+ ),
+
+ TP_printk("x86/fpu: latency:%lld RFBM:0x%llx XINUSE:0x%llx",
+ __entry->latency,
+ __entry->rfbm,
+ __entry->xinuse
+ )
+);
+
+DEFINE_EVENT(x86_fpu_latency, x86_fpu_latency_xsave,
+ TP_PROTO(struct fpstate *fpstate, u64 latency),
+ TP_ARGS(fpstate, latency)
+);
+
+DEFINE_EVENT(x86_fpu_latency, x86_fpu_latency_xrstor,
+ TP_PROTO(struct fpstate *fpstate, u64 latency),
+ TP_ARGS(fpstate, latency)
+);
+#endif
+
#undef TRACE_INCLUDE_PATH
#define TRACE_INCLUDE_PATH asm/trace/
#undef TRACE_INCLUDE_FILE
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index a4ecb04d8d64..aa997fb86537 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -5,6 +5,9 @@
#include <asm/cpufeature.h>
#include <asm/fpu/xstate.h>
#include <asm/fpu/xcr.h>
+#include <asm/trace/fpu.h>
+
+#include <linux/trace_clock.h>
#ifdef CONFIG_X86_64
DECLARE_PER_CPU(u64, xfd_state);
@@ -113,7 +116,7 @@ static inline u64 xfeatures_mask_independent(void)
* original instruction which gets replaced. We need to use it here as the
* address of the instruction where we might get an exception at.
*/
-#define XSTATE_XSAVE(st, lmask, hmask, err) \
+#define __XSTATE_XSAVE(st, lmask, hmask, err) \
asm volatile(ALTERNATIVE_3(XSAVE, \
XSAVEOPT, X86_FEATURE_XSAVEOPT, \
XSAVEC, X86_FEATURE_XSAVEC, \
@@ -130,7 +133,7 @@ static inline u64 xfeatures_mask_independent(void)
* Use XRSTORS to restore context if it is enabled. XRSTORS supports compact
* XSAVE area format.
*/
-#define XSTATE_XRESTORE(st, lmask, hmask) \
+#define __XSTATE_XRESTORE(st, lmask, hmask) \
asm volatile(ALTERNATIVE(XRSTOR, \
XRSTORS, X86_FEATURE_XSAVES) \
"\n" \
@@ -140,6 +143,35 @@ static inline u64 xfeatures_mask_independent(void)
: "D" (st), "m" (*st), "a" (lmask), "d" (hmask) \
: "memory")
+#if defined(CONFIG_X86_DEBUG_FPU)
+#define XSTATE_XSAVE(fps, lmask, hmask, err) \
+ do { \
+ struct fpstate *f = fps; \
+ u64 tc = -1; \
+ if (tracepoint_enabled(x86_fpu_latency_xsave)) \
+ tc = trace_clock(); \
+ __XSTATE_XSAVE(&f->regs.xsave, lmask, hmask, err); \
+ if (tracepoint_enabled(x86_fpu_latency_xsave)) \
+ trace_x86_fpu_latency_xsave(f, trace_clock() - tc);\
+ } while (0)
+
+#define XSTATE_XRESTORE(fps, lmask, hmask) \
+ do { \
+ struct fpstate *f = fps; \
+ u64 tc = -1; \
+ if (tracepoint_enabled(x86_fpu_latency_xrstor)) \
+ tc = trace_clock(); \
+ __XSTATE_XRESTORE(&f->regs.xsave, lmask, hmask); \
+ if (tracepoint_enabled(x86_fpu_latency_xrstor)) \
+ trace_x86_fpu_latency_xrstor(f, trace_clock() - tc);\
+ } while (0)
+#else
+#define XSTATE_XSAVE(fps, lmask, hmask, err) \
+ __XSTATE_XSAVE(&(fps)->regs.xsave, lmask, hmask, err)
+#define XSTATE_XRESTORE(fps, lmask, hmask) \
+ __XSTATE_XRESTORE(&(fps)->regs.xsave, lmask, hmask)
+#endif
+
#if defined(CONFIG_X86_64) && defined(CONFIG_X86_DEBUG_FPU)
extern void xfd_validate_state(struct fpstate *fpstate, u64 mask, bool rstor);
#else
@@ -184,7 +216,7 @@ static inline void os_xsave(struct fpstate *fpstate)
WARN_ON_FPU(!alternatives_patched);
xfd_validate_state(fpstate, mask, false);
- XSTATE_XSAVE(&fpstate->regs.xsave, lmask, hmask, err);
+ XSTATE_XSAVE(fpstate, lmask, hmask, err);
/* We should never fault when copying to a kernel buffer: */
WARN_ON_FPU(err);
@@ -201,7 +233,7 @@ static inline void os_xrstor(struct fpstate *fpstate, u64 mask)
u32 hmask = mask >> 32;
xfd_validate_state(fpstate, mask, true);
- XSTATE_XRESTORE(&fpstate->regs.xsave, lmask, hmask);
+ XSTATE_XRESTORE(fpstate, lmask, hmask);
}
/* Restore of supervisor state. Does not require XFD */
@@ -211,7 +243,7 @@ static inline void os_xrstor_supervisor(struct fpstate *fpstate)
u32 lmask = mask;
u32 hmask = mask >> 32;
- XSTATE_XRESTORE(&fpstate->regs.xsave, lmask, hmask);
+ XSTATE_XRESTORE(fpstate, lmask, hmask);
}
/*
--
2.34.1
Consume the trace log dumped by trace points x86_fpu_latency_xsave and
x86_fpu_latency_xrstor, calculate latency ranges for each RFBM and
XINUSE combination including min, max, average and 97% tail latency.
Add the average of 97% tail latency to remove the unreasonable
data which is introduced by interrupts or other noise. By adding the
experimental code disabling interrupts before the calculation of
latency, it's obvious to get the 3% tail latency has been filtered.
Make use of sqlite3 to make the data statistics more efficient and
concise. The output looks like following:
EVENTs RFBM XINUSE lat_min lat_max lat_avg lat_avg(97%)
---------------------- ------- ------ ------- ------- ------- ------------
x86_fpu_latency_xrstor 0x206e7 0x0 364 364 364 364
x86_fpu_latency_xrstor 0x206e7 0x202 112 1152 300 276
x86_fpu_latency_xsave 0x206e7 0x202 80 278 141 137
x86_fpu_latency_xsave 0x206e7 0x246 108 234 180 177
The XSAVE/XRSTOR latency trace log can be got by two ways:
1. Generated by Kernel debugfs
echo 1 > /sys/kernel/debug/tracing/events/x86_fpu/enable
cat /sys/kernel/debug/tracing/trace_pipe > trace-log
2. Generated by helper tool like 'trace-cmd'
trace-cmd record -e x86_fpu -F <command>
trace-cmd report > trace-log
Reviewed-by: Tony Luck <[email protected]>
Signed-off-by: Yi Sun <[email protected]>
diff --git a/tools/testing/fpu/xsave-latency-trace.sh b/tools/testing/fpu/xsave-latency-trace.sh
new file mode 100755
index 000000000000..d45563984fd6
--- /dev/null
+++ b/tools/testing/fpu/xsave-latency-trace.sh
@@ -0,0 +1,227 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# (c) 2022 Yi Sun <[email protected]>
+
+trace_log=$1
+trace_lat_log=".trace_lat_log"
+db_name="db_trace"
+db_file="${db_name}.db"
+table_raw="t_trace"
+table_tail="t_trace_tail"
+table_results="t_results"
+events="x86_fpu_latency_xsave|x86_fpu_latency_xrstor"
+
+# The regex for the trace log. The rough pattern:
+# (proc) (No.cpu) (flags) (timestamp): (tracepoint): latency:(123) RFBM:0x(123) XINUSE:0x(123)$
+# Fold the regex into 3 parts making it easier to read.
+regex1="([^\ ]*)[[:space:]]*\[([0-9]+)\][[:space:]]*(.....\ )?[[:space:]]*"
+regex2="([0-9.]*):[[:space:]]*([^\ :]*):.*latency:([0-9]*)[[:space:]]*"
+regex3="RFBM:(0x[0-9a-f]*)[[:space:]]*XINUSE:(0x[0-9a-f]*)$"
+
+function usage() {
+ echo "This script consumes the tracepoint data, and dumps out the"
+ echo "latency ranges for each RFBM combination."
+ echo "Usage:"
+ echo "$0 <trace-log>"
+ echo " trace-log:"
+ echo " Either generated by Kernel sysfs:"
+ echo " echo 1 > /sys/kernel/debug/tracing/events/x86_fpu/enable"
+ echo " cat /sys/kernel/debug/tracing/trace_pipe > trace-log"
+ echo ""
+ echo " Or generate by helper tool like 'trace-cmd':"
+ echo " trace-cmd record -e x86_fpu"
+ echo " trace-cmd report > trace-log"
+}
+
+# Check the dependent tools
+# {@}: a list of third-part tools
+function check_packages() {
+ for pack in "$@"; do
+ which $pack >& /dev/null
+ if [[ $? != 0 ]]; then
+ echo "Please install $pack before running this script."
+ exit 1
+ fi
+ done
+}
+
+# Run SQL command with sqlite3
+# ${*}: SQL command fed to sqlite3
+function SQL_CMD() {
+ sqlite3 $db_file "$*"
+}
+
+# Run SQL command with sqlite3 and format the output with headers and column.
+# ${*}: SQL command fed to sqlite3
+function SQL_CMD_HEADER() {
+ sqlite3 -column -header $db_file "$*"
+}
+
+# Create a table in the DB
+# ${1}： name of the table
+function create_table() {
+ if [[ "$1" == "" ]]; then
+ echo "Empty table name!"
+ exit 1
+ fi
+ SQL_CMD "create table $1 (
+ id INTEGER PRIMARY KEY AUTOINCREMENT,
+ process TEXT,
+ cpu INT,
+ timestamp FLOAT,
+ event_name TEXT,
+ lat INT,
+ RFBM INT,
+ XINUSE INT);"
+}
+
+# Round to the nearest whole number
+# ${1}: a float number
+# Output: integer
+function round() {
+ echo "scale=0; ($1+0.5)/1" | bc
+}
+
+# Insert a record in the trace table
+#
+# process cpu timestamp event_name lat RFBM XINUSE
+# $2 $3 $4 $5 $6 $7 $8
+
+function insert_line() {
+ if [[ "$1" == "" ]]; then
+ echo "Empty table name!"
+ exit 1
+ fi
+ SQL_CMD "INSERT INTO $1 (process, cpu, timestamp, event_name, lat, RFBM, XINUSE)
+ VALUES (\"$2\", $3, $4, \"$5\", $6, $7, $8);"
+}
+
+# Show the results of the trace statistics
+function get_latency_stat() {
+ SQL_CMD "create table $table_results (
+ id INTEGER PRIMARY KEY AUTOINCREMENT,
+ event_name TEXT,
+ RFBM INT,
+ XINUSE INT,
+ lat_min INT,
+ lat_max INT,
+ lat_avg INT,
+ lat_tail_avg INT);"
+
+ for((i=0; i<$cnt; i++));do
+ event_name=`get_comb_item $table_raw $i event_name`
+ RFBM=`get_comb_item $table_raw $i RFBM`
+ XINUSE=`get_comb_item $table_raw $i XINUSE`
+ lat_min=`get_comb_item $table_raw $i min\(lat\)`
+ lat_max=`get_comb_item $table_raw $i max\(lat\)`
+ lat_avg=`get_comb_item $table_raw $i avg\(lat\)`
+ lat_tail_avg=`get_comb_item $table_tail $i avg\(lat\)`
+
+ lat_avg=`round $lat_avg`
+ lat_tail_avg=`round $lat_tail_avg`
+
+ SQL_CMD "INSERT INTO $table_results
+ (event_name, RFBM,XINUSE, lat_min, lat_max, lat_avg, lat_tail_avg)
+ VALUES (\"$event_name\", $RFBM, $XINUSE, $lat_min, $lat_max,
+ $lat_avg, $lat_tail_avg);"
+ done
+
+ SQL_CMD_HEADER "select event_name[EVENTs],printf('0x%x',RFBM)[RFBM],
+ printf('0x%x',XINUSE)[XINUSE],lat_min,lat_max,lat_avg,
+ lat_tail_avg[lat_avg(97%)]
+ from $table_results;"
+}
+
+# Get the count of the combination of event_name, RFBM, XINUSE amount all lat trace records
+function get_combs_cnt() {
+ SQL_CMD "SELECT event_name, RFBM, XINUSE from $table_raw
+ group by event_name,RFBM,XINUSE;" | wc -l
+}
+
+# Get a specified combination from a table
+# ${1}: name of table
+# ${2}: the order of the combination of event_name, RFBM, XINUSE
+# ${3}: the items which are wanted to be shown
+function get_comb_item() {
+ table=$1
+ cnt=$2
+ col=$3
+ SQL_CMD "SELECT $col from $table group by event_name,RFBM,XINUSE limit $cnt,1;"
+}
+
+# Get count of the records in a given table
+# ${1}: name of the table
+function get_rows_cnt() {
+ table=$1
+ SQL_CMD "SELECT count(*) from $table;"
+}
+
+# Generate a new table from the raw trace table removing 3% tail traces.
+function gen_tail_lat() {
+ cnt=`get_combs_cnt`
+ create_table $table_tail
+
+ for((i=0; i<$cnt; i++));do
+ create_table t$i
+ event_name=`get_comb_item $table_raw $i event_name`
+ RFBM=`get_comb_item $table_raw $i RFBM`
+ XINUSE=`get_comb_item $table_raw $i XINUSE`
+
+ SQL_CMD "insert into t$i(process,cpu,timestamp,event_name,lat,RFBM,XINUSE)
+ select process,cpu,timestamp,event_name,lat,RFBM,XINUSE
+ from $table_raw where event_name=\"$event_name\" and RFBM=$RFBM and
+ XINUSE=$XINUSE ORDER BY lat ASC;"
+
+ row=`get_rows_cnt t$i`
+ row=`echo "scale=0; ($row*0.97 + 0.5)/1" | bc`
+
+ SQL_CMD "insert into $table_tail
+ (process,cpu,timestamp,event_name,lat,RFBM,XINUSE)
+ select process,cpu,timestamp,event_name,lat,RFBM,XINUSE
+ from t$i limit 0,$row;"
+ done
+
+}
+
+if [[ ! -e "$trace_log" || $# != 1 ]];then
+ usage
+ exit 1
+fi
+
+# Check dependency
+# Make sure having following packages
+check_packages sqlite3 bc wc cut
+
+# Filter trace log keeping latency related lines only
+grep -E "$events" $trace_log > $trace_lat_log
+cnt_lines=`wc -l $trace_lat_log | cut -d' ' -f1`
+# Remove the old db file if it existed before creating
+[[ -f $db_file ]] && rm -rf $db_file
+
+create_table $table_raw
+
+# Read each line from the temp file and insert into the table
+i=0
+while IFS= read -r line;
+do
+ ((i = i + 1))
+ echo -ne "(${i}/$cnt_lines) Importing trace log into database!\r"
+ if [[ "$line" =~ ${regex1}${regex2}${regex3} ]]; then
+ pname=${BASH_REMATCH[1]}
+ cpu=${BASH_REMATCH[2]}
+ ts=${BASH_REMATCH[4]}
+ ename=${BASH_REMATCH[5]}
+ lat=${BASH_REMATCH[6]}
+ ((rfbm=${BASH_REMATCH[7]}))
+ ((xinuse=${BASH_REMATCH[8]}))
+
+ insert_line $table_raw $pname $cpu $ts $ename $lat $rfbm $xinuse
+ fi
+done < $trace_lat_log
+
+gen_tail_lat
+get_latency_stat
+
+# Cleanup
+rm -rf $trace_lat_log $db_file
--
2.34.1
Show the total number of each combination of event-RFBM-XINUSE. Users can
identify which data is noise and focus more on useful data.
Signed-off-by: Yi Sun <[email protected]>
diff --git a/tools/testing/fpu/xsave-latency-trace.sh b/tools/testing/fpu/xsave-latency-trace.sh
index d45563984fd6..b2f7c3d0dd65 100755
--- a/tools/testing/fpu/xsave-latency-trace.sh
+++ b/tools/testing/fpu/xsave-latency-trace.sh
@@ -99,11 +99,14 @@ function insert_line() {
# Show the results of the trace statistics
function get_latency_stat() {
+ cnt=`get_combs_cnt`
+
SQL_CMD "create table $table_results (
id INTEGER PRIMARY KEY AUTOINCREMENT,
event_name TEXT,
RFBM INT,
XINUSE INT,
+ CNT INT,
lat_min INT,
lat_max INT,
lat_avg INT,
@@ -121,14 +124,18 @@ function get_latency_stat() {
lat_avg=`round $lat_avg`
lat_tail_avg=`round $lat_tail_avg`
+ count=`SQL_CMD "SELECT count(*) from $table_raw
+ where event_name=\"$event_name\" and RFBM=$RFBM and
+ XINUSE=$XINUSE;"`
+
SQL_CMD "INSERT INTO $table_results
- (event_name, RFBM,XINUSE, lat_min, lat_max, lat_avg, lat_tail_avg)
- VALUES (\"$event_name\", $RFBM, $XINUSE, $lat_min, $lat_max,
+ (event_name,RFBM,XINUSE, CNT, lat_min, lat_max, lat_avg, lat_tail_avg)
+ VALUES (\"$event_name\", $RFBM, $XINUSE, $count, $lat_min, $lat_max,
$lat_avg, $lat_tail_avg);"
done
SQL_CMD_HEADER "select event_name[EVENTs],printf('0x%x',RFBM)[RFBM],
- printf('0x%x',XINUSE)[XINUSE],lat_min,lat_max,lat_avg,
+ printf('0x%x',XINUSE)[XINUSE],CNT,lat_min,lat_max,lat_avg,
lat_tail_avg[lat_avg(97%)]
from $table_results;"
}
--
2.34.1