linux-kernel - [PATCH v2] perf stat: Fix JSON output formatting in iostat

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Message-ID: <20250713151224.43764-1-suchitkarunakaran@gmail.com>
Date: Sun, 13 Jul 2025 20:42:24 +0530
From: Suchit Karunakaran <suchitkarunakaran@...il.com>
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com
Cc: linux-perf-users@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	Suchit Karunakaran <suchitkarunakaran@...il.com>
Subject: [PATCH v2] perf stat: Fix JSON output formatting in iostat_prefix()

The iostat_prefix() function previously included a TODO noting that its output
format was incorrect in JSON mode. This patch corrects that by conditionally
formatting the prefix string based on the output mode specified in
perf_stat_config. Note, I didn't test it since my system doesn't support
it.

Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>
---
 tools/perf/arch/x86/util/iostat.c | 40 +++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 12 deletions(-)

Changes since v1:
- Fix issues in formatting

diff --git a/tools/perf/arch/x86/util/iostat.c b/tools/perf/arch/x86/util/iostat.c
index 7442a2cd87ed..d7ae19fb83e5 100644
--- a/tools/perf/arch/x86/util/iostat.c
+++ b/tools/perf/arch/x86/util/iostat.c
@@ -403,18 +403,34 @@ void iostat_prefix(struct evlist *evlist,
 	struct iio_root_port *rp = evlist->selected->priv;
 
 	if (rp) {
-		/*
-		 * TODO: This is the incorrect format in JSON mode.
-		 *       See prepare_timestamp()
-		 */
-		if (ts)
-			sprintf(prefix, "%6lu.%09lu%s%04x:%02x%s",
-				ts->tv_sec, ts->tv_nsec,
-				config->csv_sep, rp->domain, rp->bus,
-				config->csv_sep);
-		else
-			sprintf(prefix, "%04x:%02x%s", rp->domain, rp->bus,
-				config->csv_sep);
+		if (config->json_output) {
+			if (ts) {
+				double timestamp = ts->tv_sec + (double)ts->tv_nsec / 1e9;
+				sprintf(prefix, "{\"interval\": %.6f, \"device\": \"%04x:%02x\", ",
+					timestamp, rp->domain, rp->bus);
+			} else {
+				sprintf(prefix, "{\"device\": \"%04x:%02x\", ",
+					rp->domain, rp->bus);
+			}
+		} else if (config->csv_output) {
+			if (ts) {
+				sprintf(prefix, "%lu.%09lu%s%04x:%02x%s",
+					(unsigned long)ts->tv_sec, ts->tv_nsec,
+					config->csv_sep, rp->domain, rp->bus, config->csv_sep);
+			} else {
+				sprintf(prefix, "%04x:%02x%s",
+					rp->domain, rp->bus, config->csv_sep);
+			}
+		} else {
+			if (ts) {
+				sprintf(prefix, "%6lu.%09lu %04x:%02x ",
+					(unsigned long)ts->tv_sec, ts->tv_nsec,
+					rp->domain, rp->bus);
+			} else {
+				sprintf(prefix, "%04x:%02x ",
+					rp->domain, rp->bus);
+			}
+		}
 	}
 }
 
-- 
2.50.1