Commit f47716b7 authored by Kalesh Singh's avatar Kalesh Singh Committed by Steven Rostedt (VMware)
Browse files

tracing/histogram: Covert expr to const if both operands are constants 

If both operands of a hist trigger expression are constants, convert the
expression to a constant. This optimization avoids having to perform the
same calculation multiple times and also saves on memory since the
merged constants are represented by a single struct hist_field instead
or multiple.

Link: https://lkml.kernel.org/r/20211025200852.3002369-6-kaleshsingh@google.com



Signed-off-by: default avatarKalesh Singh <kaleshsingh@google.com>
Suggested-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent c5eac6ee

kernel/trace/trace_events_hist.c

+74 −30
Original line number Diff line number Diff line
@@ -2411,9 +2411,15 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data, 
	return ERR_PTR(ret);

}



/*

 * If the operands are var refs, return pointers the

 * variable(s) referenced in var1 and var2, else NULL.

 */

static int check_expr_operands(struct trace_array *tr,

			       struct hist_field *operand1,

			       struct hist_field *operand2)

			       struct hist_field *operand2,

			       struct hist_field **var1,

			       struct hist_field **var2)

{

	unsigned long operand1_flags = operand1->flags;

	unsigned long operand2_flags = operand2->flags;
@@ -2426,6 +2432,7 @@ static int check_expr_operands(struct trace_array *tr, 
		if (!var)

			return -EINVAL;

		operand1_flags = var->flags;

		*var1 = var;

	}



	if ((operand2_flags & HIST_FIELD_FL_VAR_REF) ||
@@ -2436,6 +2443,7 @@ static int check_expr_operands(struct trace_array *tr, 
		if (!var)

			return -EINVAL;

		operand2_flags = var->flags;

		*var2 = var;

	}



	if ((operand1_flags & HIST_FIELD_FL_TIMESTAMP_USECS) !=
@@ -2453,9 +2461,12 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data, 
				     char *var_name, unsigned int *n_subexprs)

{

	struct hist_field *operand1 = NULL, *operand2 = NULL, *expr = NULL;

	unsigned long operand_flags;

	struct hist_field *var1 = NULL, *var2 = NULL;

	unsigned long operand_flags, operand2_flags;

	int field_op, ret = -EINVAL;

	char *sep, *operand1_str;

	hist_field_fn_t op_fn;

	bool combine_consts;



	if (*n_subexprs > 3) {

		hist_err(file->tr, HIST_ERR_TOO_MANY_SUBEXPR, errpos(str));
@@ -2512,11 +2523,38 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data, 
		goto free;

	}



	ret = check_expr_operands(file->tr, operand1, operand2);

	switch (field_op) {

	case FIELD_OP_MINUS:

		op_fn = hist_field_minus;

		break;

	case FIELD_OP_PLUS:

		op_fn = hist_field_plus;

		break;

	case FIELD_OP_DIV:

		op_fn = hist_field_div;

		break;

	case FIELD_OP_MULT:

		op_fn = hist_field_mult;

		break;

	default:

		ret = -EINVAL;

		goto free;

	}



	ret = check_expr_operands(file->tr, operand1, operand2, &var1, &var2);

	if (ret)

		goto free;



	flags |= HIST_FIELD_FL_EXPR;

	operand_flags = var1 ? var1->flags : operand1->flags;

	operand2_flags = var2 ? var2->flags : operand2->flags;



	/*

	 * If both operands are constant, the expression can be

	 * collapsed to a single constant.

	 */

	combine_consts = operand_flags & operand2_flags & HIST_FIELD_FL_CONST;



	flags |= combine_consts ? HIST_FIELD_FL_CONST : HIST_FIELD_FL_EXPR;



	flags |= operand1->flags &

		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
@@ -2533,33 +2571,39 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data, 
	expr->operands[0] = operand1;

	expr->operands[1] = operand2;



	if (combine_consts) {

		if (var1)

			expr->operands[0] = var1;

		if (var2)

			expr->operands[1] = var2;



		expr->constant = op_fn(expr, NULL, NULL, NULL, NULL);



		expr->operands[0] = NULL;

		expr->operands[1] = NULL;



		/*

		 * var refs won't be destroyed immediately

		 * See: destroy_hist_field()

		 */

		destroy_hist_field(operand2, 0);

		destroy_hist_field(operand1, 0);



		expr->name = expr_str(expr, 0);

	} else {

		expr->fn = op_fn;



		/* The operand sizes should be the same, so just pick one */

		expr->size = operand1->size;



		expr->operator = field_op;

	expr->name = expr_str(expr, 0);

		expr->type = kstrdup_const(operand1->type, GFP_KERNEL);

		if (!expr->type) {

			ret = -ENOMEM;

			goto free;

		}



	switch (field_op) {

	case FIELD_OP_MINUS:

		expr->fn = hist_field_minus;

		break;

	case FIELD_OP_PLUS:

		expr->fn = hist_field_plus;

		break;

	case FIELD_OP_DIV:

		expr->fn = hist_field_div;

		break;

	case FIELD_OP_MULT:

		expr->fn = hist_field_mult;

		break;

	default:

		ret = -EINVAL;

		goto free;

		expr->name = expr_str(expr, 0);

	}



	return expr;