linux-kernel - [PATCH v5 3/3] coresight: tmc: Decouple the perf buffer allocation from sysfs mode

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Message-ID: <20260121101543.2017014-4-wangyushan12@huawei.com>
Date: Wed, 21 Jan 2026 18:15:43 +0800
From: Yushan Wang <wangyushan12@...wei.com>
To: <suzuki.poulose@....com>, <james.clark@...aro.org>,
	<anshuman.khandual@....com>, <yeoreum.yun@....com>, <mike.leach@...aro.org>,
	<leo.yan@....com>
CC: <coresight@...ts.linaro.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
	<jonathan.cameron@...wei.com>, <hejunhao3@...artners.com>,
	<wangyushan12@...wei.com>
Subject: [PATCH v5 3/3] coresight: tmc: Decouple the perf buffer allocation from sysfs mode

From: Yicong Yang <yangyicong@...ilicon.com>

Currently the perf buffer allocation follows the below logic:
- if the required AUX buffer size if larger, allocate the buffer with
  the required size
- otherwise allocate the size reference to the sysfs buffer size

This is not useful as we only collect to one AUX data, so just try to
allocate the buffer match the AUX buffer size.

Suggested-by: Suzuki K Poulose <suzuki.poulose@....com>
Link: https://lore.kernel.org/linux-arm-kernel/df8967cd-2157-46a2-97d9-a1aea883cf63@arm.com/
Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
Signed-off-by: Junhao He <hejunhao3@...artners.com>
---
 .../hwtracing/coresight/coresight-tmc-etr.c   | 30 ++++++-------------
 1 file changed, 9 insertions(+), 21 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index fc0a946053dd..cee82e52c4ea 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1367,9 +1367,7 @@ EXPORT_SYMBOL_GPL(tmc_etr_get_buffer);
 
 /*
  * alloc_etr_buf: Allocate ETR buffer for use by perf.
- * The size of the hardware buffer is dependent on the size configured
- * via sysfs and the perf ring buffer size. We prefer to allocate the
- * largest possible size, scaling down the size by half until it
+ * Allocate the largest possible size, scaling down the size by half until it
  * reaches a minimum limit (1M), beyond which we give up.
  */
 static struct etr_buf *
@@ -1378,36 +1376,26 @@ alloc_etr_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
 {
 	int node;
 	struct etr_buf *etr_buf;
-	unsigned long size;
+	ssize_t size;
 
 	node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu);
-	/*
-	 * Try to match the perf ring buffer size if it is larger
-	 * than the size requested via sysfs.
-	 */
-	if ((nr_pages << PAGE_SHIFT) > drvdata->size) {
-		etr_buf = tmc_alloc_etr_buf(drvdata, ((ssize_t)nr_pages << PAGE_SHIFT),
-					    0, node, NULL);
-		if (!IS_ERR(etr_buf))
-			goto done;
-	}
+
+	/* Use the minimum limit if the required size is smaller */
+	size = nr_pages << PAGE_SHIFT;
+	size = max_t(ssize_t, size, TMC_ETR_PERF_MIN_BUF_SIZE);
 
 	/*
-	 * Else switch to configured size for this ETR
-	 * and scale down until we hit the minimum limit.
+	 * Try to allocate the required size for this ETR, if failed scale
+	 * down until we hit the minimum limit.
 	 */
-	size = drvdata->size;
 	do {
 		etr_buf = tmc_alloc_etr_buf(drvdata, size, 0, node, NULL);
 		if (!IS_ERR(etr_buf))
-			goto done;
+			return etr_buf;
 		size /= 2;
 	} while (size >= TMC_ETR_PERF_MIN_BUF_SIZE);
 
 	return ERR_PTR(-ENOMEM);
-
-done:
-	return etr_buf;
 }
 
 static struct etr_buf *
-- 
2.33.0