linux-kernel - [PATCH v2 01/15] blktrace: only calculate trace length once

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Message-ID: <20250925150231.67342-2-johannes.thumshirn@wdc.com>
Date: Thu, 25 Sep 2025 17:02:17 +0200
From: Johannes Thumshirn <johannes.thumshirn@....com>
To: Jens Axboe <axboe@...nel.dk>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-btrace@...r.kernel.org,
	John Garry <john.g.garry@...cle.com>,
	Hannes Reinecke <hare@...e.de>,
	Damien Le Moal <dlemoal@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Naohiro Aota <naohiro.aota@....com>,
	Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
	Chaitanya Kulkarni <chaitanyak@...dia.com>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	Johannes Thumshirn <johannes.thumshirn@....com>
Subject: [PATCH v2 01/15] blktrace: only calculate trace length once

De-duplicate the calculation of the trace length instead of doing the
calculation twice, once for calling trace_buffer_lock_reserve() and once
for calling relay_reserve().

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
---
 kernel/trace/blktrace.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 6941145b5058..bc4b885f2cec 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -76,13 +76,14 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 	int cpu = smp_processor_id();
 	bool blk_tracer = blk_tracer_enabled;
 	ssize_t cgid_len = cgid ? sizeof(cgid) : 0;
+	size_t trace_len;
 
+	trace_len = sizeof(*t) + cgid_len + len;
 	if (blk_tracer) {
 		buffer = blk_tr->array_buffer.buffer;
 		trace_ctx = tracing_gen_ctx_flags(0);
 		event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
-						  sizeof(*t) + len + cgid_len,
-						  trace_ctx);
+						  trace_len, trace_ctx);
 		if (!event)
 			return;
 		t = ring_buffer_event_data(event);
@@ -92,7 +93,7 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 	if (!bt->rchan)
 		return;
 
-	t = relay_reserve(bt->rchan, sizeof(*t) + len + cgid_len);
+	t = relay_reserve(bt->rchan, trace_len);
 	if (t) {
 		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
 		t->time = ktime_to_ns(ktime_get());
@@ -228,6 +229,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	bool blk_tracer = blk_tracer_enabled;
 	ssize_t cgid_len = cgid ? sizeof(cgid) : 0;
 	const enum req_op op = opf & REQ_OP_MASK;
+	size_t trace_len;
 
 	if (unlikely(bt->trace_state != Blktrace_running && !blk_tracer))
 		return;
@@ -250,14 +252,14 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 		return;
 	cpu = raw_smp_processor_id();
 
+	trace_len = sizeof(*t) + pdu_len + cgid_len;
 	if (blk_tracer) {
 		tracing_record_cmdline(current);
 
 		buffer = blk_tr->array_buffer.buffer;
 		trace_ctx = tracing_gen_ctx_flags(0);
 		event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
-						  sizeof(*t) + pdu_len + cgid_len,
-						  trace_ctx);
+						  trace_len, trace_ctx);
 		if (!event)
 			return;
 		t = ring_buffer_event_data(event);
@@ -273,7 +275,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	 * from coming in and stepping on our toes.
 	 */
 	local_irq_save(flags);
-	t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len + cgid_len);
+	t = relay_reserve(bt->rchan, trace_len);
 	if (t) {
 		sequence = per_cpu_ptr(bt->sequence, cpu);
 
-- 
2.51.0