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ftrace

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Matthias Schiffer 2018-03-25 13:29:20 +02:00
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patches/lede/0068-generic-add-ftrace-fixes.patch Normal file
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@ -0,0 +1,284 @@
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sat, 24 Mar 2018 18:32:33 +0100
Subject: generic: add ftrace fixes
diff --git a/target/linux/generic/patches-4.4/800-0001-ftrace-fix-stddev-calculation-in-function-profiler-a.patch b/target/linux/generic/patches-4.4/800-0001-ftrace-fix-stddev-calculation-in-function-profiler-a.patch
new file mode 100644
index 0000000000000000000000000000000000000000..58f109414596fb2407d9392313f57b43805ff6d0
--- /dev/null
+++ b/target/linux/generic/patches-4.4/800-0001-ftrace-fix-stddev-calculation-in-function-profiler-a.patch
@@ -0,0 +1,123 @@
+From f208c5c360f1e86327b0adbb879d61f4779e8ddd Mon Sep 17 00:00:00 2001
+Message-Id: <f208c5c360f1e86327b0adbb879d61f4779e8ddd.1521912248.git.mschiffer@universe-factory.net>
+From: Matthias Schiffer <mschiffer@universe-factory.net>
+Date: Sat, 24 Mar 2018 16:54:16 +0100
+Subject: [PATCH 1/2] ftrace: fix stddev calculation in function profiler
+ (again)
+
+It is well-known that it is not possible to accurately calculate variances
+just by accumulating squared samples; in fact, such an approach can even
+result in negative numbers. An earlier attempt to fix the calculation
+referred to Welford's method, but did not implement it correctly, leading
+to meeaningless output like the following:
+
+ nf_conntrack_proto_fini 50 373.523 us 7.470 us 3234315951 us
+
+Welford's method uses one do_div() in the tracing path; this cannot be
+avoided. The average time is added to struct ftrace_profile, so only a
+single division is required. I also considered the following alternatives:
+
+1) Only keeping the avg field and removing the aggregated time would
+greatly lead to severe rounding errors in calculating the total time based
+on counter and avg.
+
+2) Calculating both the old and the new average in profile_graph_return()
+instead of storing it in struct ftrace_profile would require a second
+division.
+
+3) I managed to transform Welford's equations in a way that uses the total
+time instead of the average and requires only a single division.
+Unfortunately, the divisor is counter^3 in this case, easily overflowing
+even 64bit integers.
+
+Ruling out the above alternatives, I chose the present approach to fix the
+issue.
+
+Fixes: e330b3bcd831 ("tracing: Show sample std dev in function profiling")
+Fixes: 52d85d763086 ("ftrace: Fix stddev calculation in function profiler")
+Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
+---
+ kernel/trace/ftrace.c | 33 +++++++++++++++++++--------------
+ 1 file changed, 19 insertions(+), 14 deletions(-)
+
+--- a/kernel/trace/ftrace.c
++++ b/kernel/trace/ftrace.c
+@@ -504,7 +504,8 @@ struct ftrace_profile {
+ unsigned long counter;
+ #ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ unsigned long long time;
+- unsigned long long time_squared;
++ unsigned long long avg;
++ unsigned long long stddev;
+ #endif
+ };
+
+@@ -624,7 +625,6 @@ static int function_stat_show(struct seq
+ int ret = 0;
+ #ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ static struct trace_seq s;
+- unsigned long long avg;
+ unsigned long long stddev;
+ #endif
+ mutex_lock(&ftrace_profile_lock);
+@@ -636,9 +636,7 @@ static int function_stat_show(struct seq
+ }
+
+ #ifdef CONFIG_FUNCTION_GRAPH_TRACER
+- avg = rec->time;
+- do_div(avg, rec->counter);
+- if (tracing_thresh && (avg < tracing_thresh))
++ if (tracing_thresh && (rec->avg < tracing_thresh))
+ goto out;
+ #endif
+
+@@ -652,24 +650,19 @@ static int function_stat_show(struct seq
+ if (rec->counter <= 1)
+ stddev = 0;
+ else {
+- /*
+- * Apply Welford's method:
+- * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
+- */
+- stddev = rec->counter * rec->time_squared -
+- rec->time * rec->time;
++ stddev = rec->stddev;
+
+ /*
+ * Divide only 1000 for ns^2 -> us^2 conversion.
+ * trace_print_graph_duration will divide 1000 again.
+ */
+- do_div(stddev, rec->counter * (rec->counter - 1) * 1000);
++ do_div(stddev, 1000 * (rec->counter - 1));
+ }
+
+ trace_seq_init(&s);
+ trace_print_graph_duration(rec->time, &s);
+ trace_seq_puts(&s, " ");
+- trace_print_graph_duration(avg, &s);
++ trace_print_graph_duration(rec->avg, &s);
+ trace_seq_puts(&s, " ");
+ trace_print_graph_duration(stddev, &s);
+ trace_print_seq(m, &s);
+@@ -939,8 +932,20 @@ static void profile_graph_return(struct
+
+ rec = ftrace_find_profiled_func(stat, trace->func);
+ if (rec) {
++ unsigned long long avg, delta1, delta2;
++
+ rec->time += calltime;
+- rec->time_squared += calltime * calltime;
++
++ /* Apply Welford's method */
++ delta1 = calltime - rec->avg;
++
++ avg = rec->time;
++ do_div(avg, rec->counter);
++ rec->avg = avg;
++
++ delta2 = calltime - rec->avg;
++
++ rec->stddev += delta1 * delta2;
+ }
+
+ out:
diff --git a/target/linux/generic/patches-4.4/800-0002-mips-ftrace-fix-static-function-graph-tracing.patch b/target/linux/generic/patches-4.4/800-0002-mips-ftrace-fix-static-function-graph-tracing.patch
new file mode 100644
index 0000000000000000000000000000000000000000..06c32b62cc4a7ccd05bff984c3e9646258a0cf8f
--- /dev/null
+++ b/target/linux/generic/patches-4.4/800-0002-mips-ftrace-fix-static-function-graph-tracing.patch
@@ -0,0 +1,73 @@
+From 7dc2bb7f712c1e3cfeaafaefe3a3f97668dee549 Mon Sep 17 00:00:00 2001
+Message-Id: <7dc2bb7f712c1e3cfeaafaefe3a3f97668dee549.1521912248.git.mschiffer@universe-factory.net>
+In-Reply-To: <f208c5c360f1e86327b0adbb879d61f4779e8ddd.1521912248.git.mschiffer@universe-factory.net>
+References: <f208c5c360f1e86327b0adbb879d61f4779e8ddd.1521912248.git.mschiffer@universe-factory.net>
+From: Matthias Schiffer <mschiffer@universe-factory.net>
+Date: Sat, 24 Mar 2018 16:50:05 +0100
+Subject: [PATCH 2/2] mips: ftrace: fix static function graph tracing
+
+ftrace_graph_caller was never run after calling ftrace_trace_function,
+breaking the function graph tracer. Fix this to bring it in line with the
+x86 implementation.
+
+While we're at it, also streamline the control flow of _mcount a bit to
+reduce the number of branches.
+
+This issue was reported before:
+https://www.linux-mips.org/archives/linux-mips/2014-11/msg00295.html
+
+Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
+---
+ arch/mips/kernel/mcount.S | 27 ++++++++++++---------------
+ 1 file changed, 12 insertions(+), 15 deletions(-)
+
+--- a/arch/mips/kernel/mcount.S
++++ b/arch/mips/kernel/mcount.S
+@@ -116,10 +116,20 @@ ftrace_stub:
+ NESTED(_mcount, PT_SIZE, ra)
+ PTR_LA t1, ftrace_stub
+ PTR_L t2, ftrace_trace_function /* Prepare t2 for (1) */
+- bne t1, t2, static_trace
++ beq t1, t2, fgraph_trace
+ nop
+
++ MCOUNT_SAVE_REGS
++
++ move a0, ra /* arg1: self return address */
++ jalr t2 /* (1) call *ftrace_trace_function */
++ move a1, AT /* arg2: parent's return address */
++
++ MCOUNT_RESTORE_REGS
++
++fgraph_trace:
+ #ifdef CONFIG_FUNCTION_GRAPH_TRACER
++ PTR_LA t1, ftrace_stub
+ PTR_L t3, ftrace_graph_return
+ bne t1, t3, ftrace_graph_caller
+ nop
+@@ -128,24 +138,11 @@ NESTED(_mcount, PT_SIZE, ra)
+ bne t1, t3, ftrace_graph_caller
+ nop
+ #endif
+- b ftrace_stub
+-#ifdef CONFIG_32BIT
+- addiu sp, sp, 8
+-#else
+- nop
+-#endif
+-
+-static_trace:
+- MCOUNT_SAVE_REGS
+-
+- move a0, ra /* arg1: self return address */
+- jalr t2 /* (1) call *ftrace_trace_function */
+- move a1, AT /* arg2: parent's return address */
+
+- MCOUNT_RESTORE_REGS
+ #ifdef CONFIG_32BIT
+ addiu sp, sp, 8
+ #endif
++
+ .globl ftrace_stub
+ ftrace_stub:
+ RETURN_BACK
diff --git a/target/linux/generic/patches-4.4/801-ftrace-fixes.patch b/target/linux/generic/patches-4.4/801-ftrace-fixes.patch
new file mode 100644
index 0000000000000000000000000000000000000000..0390c0c70b3354d9f058dca96a985f499d506df5
--- /dev/null
+++ b/target/linux/generic/patches-4.4/801-ftrace-fixes.patch
@@ -0,0 +1,66 @@
+--- a/kernel/trace/ftrace.c
++++ b/kernel/trace/ftrace.c
+@@ -473,8 +473,9 @@ static void ftrace_update_pid_func(void)
+ struct ftrace_profile {
+ struct hlist_node node;
+ unsigned long ip;
+- unsigned long counter;
++ unsigned long long counter;
+ #ifdef CONFIG_FUNCTION_GRAPH_TRACER
++ unsigned long long returns;
+ unsigned long long time;
+ unsigned long long avg;
+ unsigned long long stddev;
+@@ -613,7 +614,7 @@ static int function_stat_show(struct seq
+ #endif
+
+ kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
+- seq_printf(m, " %-30.30s %10lu", str, rec->counter);
++ seq_printf(m, " %-30.30s %10llu", str, rec->counter);
+
+ #ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ seq_puts(m, " ");
+@@ -916,13 +917,15 @@ static void profile_graph_return(struct
+ if (rec) {
+ unsigned long long avg, delta1, delta2;
+
++ rec->returns++;
++
+ rec->time += calltime;
+
+ /* Apply Welford's method */
+ delta1 = calltime - rec->avg;
+
+ avg = rec->time;
+- do_div(avg, rec->counter);
++ do_div(avg, rec->returns);
+ rec->avg = avg;
+
+ delta2 = calltime - rec->avg;
+--- a/arch/mips/kernel/ftrace.c
++++ b/arch/mips/kernel/ftrace.c
+@@ -338,7 +338,7 @@ void prepare_ftrace_return(unsigned long
+ struct ftrace_graph_ent trace;
+ unsigned long return_hooker = (unsigned long)
+ &return_to_handler;
+- int faulted, insns;
++ int faulted;
+
+ if (unlikely(ftrace_graph_is_dead()))
+ return;
+@@ -388,14 +388,7 @@ void prepare_ftrace_return(unsigned long
+ return;
+ }
+
+- /*
+- * Get the recorded ip of the current mcount calling site in the
+- * __mcount_loc section, which will be used to filter the function
+- * entries configured through the tracing/set_graph_function interface.
+- */
+-
+- insns = in_kernel_space(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
+- trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);
++ trace.func = self_ra;
+
+ /* Only trace if the calling function expects to */
+ if (!ftrace_graph_entry(&trace)) {

5
targets/generic
View File

@ -23,6 +23,11 @@ config '# CONFIG_BUSYBOX_CONFIG_FEATURE_PREFER_IPV4_ADDRESS is not set'
config 'CONFIG_PACKAGE_ATH_DEBUG=y'
config 'CONFIG_KERNEL_FTRACE=y'
config 'CONFIG_KERNEL_FUNCTION_TRACER=y'
config 'CONFIG_KERNEL_FUNCTION_GRAPH_TRACER=y'
config 'CONFIG_KERNEL_FUNCTION_PROFILER=y'
try_config 'CONFIG_TARGET_MULTI_PROFILE=y'
try_config 'CONFIG_TARGET_PER_DEVICE_ROOTFS=y'