Merge tag 'trace-v5.16-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull more tracing updates from Steven Rostedt:

 - osnoise and timerlat updates that will work with the RTLA tool
   (Real-Time Linux Analysis).

   Specifically it disconnects the work load (threads that look for
   latency) from the tracing instances attached to them, allowing for
   more than one instance to retrieve data from the work load.

 - Optimization on division in the trace histogram trigger code to use
   shift and multiply when possible. Also added documentation.

 - Fix prototype to my_direct_func in direct ftrace trampoline sample
   code.

* tag 'trace-v5.16-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ftrace/samples: Add missing prototype for my_direct_func
  tracing/selftests: Add tests for hist trigger expression parsing
  tracing/histogram: Document hist trigger variables
  tracing/histogram: Update division by 0 documentation
  tracing/histogram: Optimize division by constants
  tracing/osnoise: Remove PREEMPT_RT ifdefs from inside functions
  tracing/osnoise: Remove STACKTRACE ifdefs from inside functions
  tracing/osnoise: Allow multiple instances of the same tracer
  tracing/osnoise: Remove TIMERLAT ifdefs from inside functions
  tracing/osnoise: Support a list of trace_array *tr
  tracing/osnoise: Use start/stop_per_cpu_kthreads() on osnoise_cpus_write()
  tracing/osnoise: Split workload start from the tracer start
  tracing/osnoise: Improve comments about barrier need for NMI callbacks
  tracing/osnoise: Do not follow tracing_cpumask

Author: torvalds

Documentation/trace/histogram.rst

@@ -1766,7 +1766,8 @@ using the same key and variable from yet another event::
 Expressions support the use of addition, subtraction, multiplication and
 division operators (+-\*/).
 
-Note that division by zero always returns -1.
+Note if division by zero cannot be detected at parse time (i.e. the
+divisor is not a constant), the result will be -1.
 
 Numeric constants can also be used directly in an expression::
 

kernel/trace/trace.c

@@ -5605,6 +5605,7 @@ static const char readme_msg[] =
 #ifdef CONFIG_HIST_TRIGGERS
 	"      hist trigger\t- If set, event hits are aggregated into a hash table\n"
 	"\t    Format: hist:keys=<field1[,field2,...]>\n"
+	"\t            [:<var1>=<field|var_ref|numeric_literal>[,<var2>=...]]\n"
 	"\t            [:values=<field1[,field2,...]>]\n"
 	"\t            [:sort=<field1[,field2,...]>]\n"
 	"\t            [:size=#entries]\n"
@@ -5616,6 +5617,16 @@ static const char readme_msg[] =
 	"\t            common_timestamp - to record current timestamp\n"
 	"\t            common_cpu - to record the CPU the event happened on\n"
 	"\n"
+	"\t    A hist trigger variable can be:\n"
+	"\t        - a reference to a field e.g. x=current_timestamp,\n"
+	"\t        - a reference to another variable e.g. y=$x,\n"
+	"\t        - a numeric literal: e.g. ms_per_sec=1000,\n"
+	"\t        - an arithmetic expression: e.g. time_secs=current_timestamp/1000\n"
+	"\n"
+	"\t    hist trigger aritmethic expressions support addition(+), subtraction(-),\n"
+	"\t    multiplication(*) and division(/) operators. An operand can be either a\n"
+	"\t    variable reference, field or numeric literal.\n"
+	"\n"
 	"\t    When a matching event is hit, an entry is added to a hash\n"
 	"\t    table using the key(s) and value(s) named, and the value of a\n"
 	"\t    sum called 'hitcount' is incremented.  Keys and values\n"

kernel/trace/trace_events_hist.c

@@ -68,7 +68,8 @@
 	C(INVALID_SORT_FIELD,	"Sort field must be a key or a val"),	\
 	C(INVALID_STR_OPERAND,	"String type can not be an operand in expression"), \
 	C(EXPECT_NUMBER,	"Expecting numeric literal"),		\
-	C(UNARY_MINUS_SUBEXPR,	"Unary minus not supported in sub-expressions"),
+	C(UNARY_MINUS_SUBEXPR,	"Unary minus not supported in sub-expressions"), \
+	C(DIVISION_BY_ZERO,	"Division by zero"),
 
 #undef C
 #define C(a, b)		HIST_ERR_##a
@@ -92,6 +93,7 @@ typedef u64 (*hist_field_fn_t) (struct hist_field *field,
 #define HIST_FIELDS_MAX		(TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
 #define HIST_ACTIONS_MAX	8
 #define HIST_CONST_DIGITS_MAX	21
+#define HIST_DIV_SHIFT		20  /* For optimizing division by constants */
 
 enum field_op_id {
 	FIELD_OP_NONE,
@@ -160,6 +162,8 @@ struct hist_field {
 
 	/* Numeric literals are represented as u64 */
 	u64				constant;
+	/* Used to optimize division by constants */
+	u64				div_multiplier;
 };
 
 static u64 hist_field_none(struct hist_field *field,
@@ -311,6 +315,68 @@ static u64 hist_field_div(struct hist_field *hist_field,
 	return div64_u64(val1, val2);
 }
 
+static u64 div_by_power_of_two(struct hist_field *hist_field,
+				struct tracing_map_elt *elt,
+				struct trace_buffer *buffer,
+				struct ring_buffer_event *rbe,
+				void *event)
+{
+	struct hist_field *operand1 = hist_field->operands[0];
+	struct hist_field *operand2 = hist_field->operands[1];
+
+	u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
+
+	return val1 >> __ffs64(operand2->constant);
+}
+
+static u64 div_by_not_power_of_two(struct hist_field *hist_field,
+				struct tracing_map_elt *elt,
+				struct trace_buffer *buffer,
+				struct ring_buffer_event *rbe,
+				void *event)
+{
+	struct hist_field *operand1 = hist_field->operands[0];
+	struct hist_field *operand2 = hist_field->operands[1];
+
+	u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
+
+	return div64_u64(val1, operand2->constant);
+}
+
+static u64 div_by_mult_and_shift(struct hist_field *hist_field,
+				struct tracing_map_elt *elt,
+				struct trace_buffer *buffer,
+				struct ring_buffer_event *rbe,
+				void *event)
+{
+	struct hist_field *operand1 = hist_field->operands[0];
+	struct hist_field *operand2 = hist_field->operands[1];
+
+	u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
+
+	/*
+	 * If the divisor is a constant, do a multiplication and shift instead.
+	 *
+	 * Choose Z = some power of 2. If Y <= Z, then:
+	 *     X / Y = (X * (Z / Y)) / Z
+	 *
+	 * (Z / Y) is a constant (mult) which is calculated at parse time, so:
+	 *     X / Y = (X * mult) / Z
+	 *
+	 * The division by Z can be replaced by a shift since Z is a power of 2:
+	 *     X / Y = (X * mult) >> HIST_DIV_SHIFT
+	 *
+	 * As long, as X < Z the results will not be off by more than 1.
+	 */
+	if (val1 < (1 << HIST_DIV_SHIFT)) {
+		u64 mult = operand2->div_multiplier;
+
+		return (val1 * mult + ((1 << HIST_DIV_SHIFT) - 1)) >> HIST_DIV_SHIFT;
+	}
+
+	return div64_u64(val1, operand2->constant);
+}
+
 static u64 hist_field_mult(struct hist_field *hist_field,
 			   struct tracing_map_elt *elt,
 			   struct trace_buffer *buffer,
@@ -573,6 +639,25 @@ struct snapshot_context {
 	void			*key;
 };
 
+/*
+ * Returns the specific division function to use if the divisor
+ * is constant. This avoids extra branches when the trigger is hit.
+ */
+static hist_field_fn_t hist_field_get_div_fn(struct hist_field *divisor)
+{
+	u64 div = divisor->constant;
+
+	if (!(div & (div - 1)))
+		return div_by_power_of_two;
+
+	/* If the divisor is too large, do a regular division */
+	if (div > (1 << HIST_DIV_SHIFT))
+		return div_by_not_power_of_two;
+
+	divisor->div_multiplier = div64_u64((u64)(1 << HIST_DIV_SHIFT), div);
+	return div_by_mult_and_shift;
+}
+
 static void track_data_free(struct track_data *track_data)
 {
 	struct hist_elt_data *elt_data;
@@ -2575,6 +2660,24 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 	expr->operands[0] = operand1;
 	expr->operands[1] = operand2;
 
+	if (field_op == FIELD_OP_DIV &&
+			operand2_flags & HIST_FIELD_FL_CONST) {
+		u64 divisor = var2 ? var2->constant : operand2->constant;
+
+		if (!divisor) {
+			hist_err(file->tr, HIST_ERR_DIVISION_BY_ZERO, errpos(str));
+			ret = -EDOM;
+			goto free;
+		}
+
+		/*
+		 * Copy the divisor here so we don't have to look it up
+		 * later if this is a var ref
+		 */
+		operand2->constant = divisor;
+		op_fn = hist_field_get_div_fn(operand2);
+	}
+
 	if (combine_consts) {
 		if (var1)
 			expr->operands[0] = var1;