[PATCH 6.1.y 3/3] asm-generic/io.h: Skip trace helpers if rwmmio events are disabled

16 Oct 2025

From: Varad Gautam varadgautam@google.com
[ Upstream commit 8327bd4fcb6c1dab01ce5c6ff00b42496836dcd2 ]
With `CONFIG_TRACE_MMIO_ACCESS=y`, the `{read,write}{b,w,l,q}{_relaxed}()`
mmio accessors unconditionally call `log_{post_}{read,write}_mmio()`
helpers, which in turn call the ftrace ops for `rwmmio` trace events
This adds a performance penalty per mmio accessor call, even when
`rwmmio` events are disabled at runtime (~80% overhead on local
measurement).
Guard these with `tracepoint_enabled()`.
Signed-off-by: Varad Gautam varadgautam@google.com
Fixes: 210031971cdd ("asm-generic/io: Add logging support for MMIO accessors")
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann arnd@arndb.de
Signed-off-by: Sasha Levin sashal@kernel.org
---
 include/asm-generic/io.h | 98 +++++++++++++++++++++++++++-------------
 1 file changed, 66 insertions(+), 32 deletions(-)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index 587e7e9b9a375..b5c5aa25bb8bf 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -74,6 +74,7 @@
 #if IS_ENABLED(CONFIG_TRACE_MMIO_ACCESS) && !(defined(__DISABLE_TRACE_MMIO__))
 #include <linux/tracepoint-defs.h>
+#define rwmmio_tracepoint_enabled(tracepoint) tracepoint_enabled(tracepoint)
 DECLARE_TRACEPOINT(rwmmio_write);
 DECLARE_TRACEPOINT(rwmmio_post_write);
 DECLARE_TRACEPOINT(rwmmio_read);
@@ -90,6 +91,7 @@ void log_post_read_mmio(u64 val, u8 width, const volatile void __iomem *addr,
#else
+#define rwmmio_tracepoint_enabled(tracepoint) false
 static inline void log_write_mmio(u64 val, u8 width, volatile void __iomem *addr,
    			  unsigned long caller_addr, unsigned long caller_addr0) {}
 static inline void log_post_write_mmio(u64 val, u8 width, volatile void __iomem *addr,
@@ -188,11 +190,13 @@ static inline u8 readb(const volatile void __iomem *addr)
 {
    u8 val;
-	log_read_mmio(8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(8, addr, _THIS_IP_, _RET_IP_);
    __io_br();
    val = __raw_readb(addr);
    __io_ar(val);
-	log_post_read_mmio(val, 8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 8, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -203,11 +207,13 @@ static inline u16 readw(const volatile void __iomem *addr)
 {
    u16 val;
-	log_read_mmio(16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(16, addr, _THIS_IP_, _RET_IP_);
    __io_br();
    val = __le16_to_cpu((__le16 __force)__raw_readw(addr));
    __io_ar(val);
-	log_post_read_mmio(val, 16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 16, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -218,11 +224,13 @@ static inline u32 readl(const volatile void __iomem *addr)
 {
    u32 val;
-	log_read_mmio(32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(32, addr, _THIS_IP_, _RET_IP_);
    __io_br();
    val = __le32_to_cpu((__le32 __force)__raw_readl(addr));
    __io_ar(val);
-	log_post_read_mmio(val, 32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 32, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -234,11 +242,13 @@ static inline u64 readq(const volatile void __iomem *addr)
 {
    u64 val;
-	log_read_mmio(64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(64, addr, _THIS_IP_, _RET_IP_);
    __io_br();
    val = __le64_to_cpu((__le64 __force)__raw_readq(addr));
    __io_ar(val);
-	log_post_read_mmio(val, 64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 64, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -248,11 +258,13 @@ static inline u64 readq(const volatile void __iomem *addr)
 #define writeb writeb
 static inline void writeb(u8 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
    __io_bw();
    __raw_writeb(value, addr);
    __io_aw();
-	log_post_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
@@ -260,11 +272,13 @@ static inline void writeb(u8 value, volatile void __iomem *addr)
 #define writew writew
 static inline void writew(u16 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
    __io_bw();
    __raw_writew((u16 __force)cpu_to_le16(value), addr);
    __io_aw();
-	log_post_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
@@ -272,11 +286,13 @@ static inline void writew(u16 value, volatile void __iomem *addr)
 #define writel writel
 static inline void writel(u32 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
    __io_bw();
    __raw_writel((u32 __force)__cpu_to_le32(value), addr);
    __io_aw();
-	log_post_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
@@ -285,11 +301,13 @@ static inline void writel(u32 value, volatile void __iomem *addr)
 #define writeq writeq
 static inline void writeq(u64 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
    __io_bw();
    __raw_writeq((u64 __force)__cpu_to_le64(value), addr);
    __io_aw();
-	log_post_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
 #endif /* CONFIG_64BIT */
@@ -305,9 +323,11 @@ static inline u8 readb_relaxed(const volatile void __iomem *addr)
 {
    u8 val;
-	log_read_mmio(8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(8, addr, _THIS_IP_, _RET_IP_);
    val = __raw_readb(addr);
-	log_post_read_mmio(val, 8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 8, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -318,9 +338,11 @@ static inline u16 readw_relaxed(const volatile void __iomem *addr)
 {
    u16 val;
-	log_read_mmio(16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(16, addr, _THIS_IP_, _RET_IP_);
    val = __le16_to_cpu((__le16 __force)__raw_readw(addr));
-	log_post_read_mmio(val, 16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 16, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -331,9 +353,11 @@ static inline u32 readl_relaxed(const volatile void __iomem *addr)
 {
    u32 val;
-	log_read_mmio(32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(32, addr, _THIS_IP_, _RET_IP_);
    val = __le32_to_cpu((__le32 __force)__raw_readl(addr));
-	log_post_read_mmio(val, 32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 32, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -344,9 +368,11 @@ static inline u64 readq_relaxed(const volatile void __iomem *addr)
 {
    u64 val;
-	log_read_mmio(64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_read))
+		log_read_mmio(64, addr, _THIS_IP_, _RET_IP_);
    val = __le64_to_cpu((__le64 __force)__raw_readq(addr));
-	log_post_read_mmio(val, 64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_read))
+		log_post_read_mmio(val, 64, addr, _THIS_IP_, _RET_IP_);
    return val;
 }
 #endif
@@ -355,9 +381,11 @@ static inline u64 readq_relaxed(const volatile void __iomem *addr)
 #define writeb_relaxed writeb_relaxed
 static inline void writeb_relaxed(u8 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
    __raw_writeb(value, addr);
-	log_post_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 8, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
@@ -365,9 +393,11 @@ static inline void writeb_relaxed(u8 value, volatile void __iomem *addr)
 #define writew_relaxed writew_relaxed
 static inline void writew_relaxed(u16 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
    __raw_writew((u16 __force)cpu_to_le16(value), addr);
-	log_post_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 16, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
@@ -375,9 +405,11 @@ static inline void writew_relaxed(u16 value, volatile void __iomem *addr)
 #define writel_relaxed writel_relaxed
 static inline void writel_relaxed(u32 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
    __raw_writel((u32 __force)__cpu_to_le32(value), addr);
-	log_post_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 32, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
@@ -385,9 +417,11 @@ static inline void writel_relaxed(u32 value, volatile void __iomem *addr)
 #define writeq_relaxed writeq_relaxed
 static inline void writeq_relaxed(u64 value, volatile void __iomem *addr)
 {
-	log_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_write))
+		log_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
    __raw_writeq((u64 __force)__cpu_to_le64(value), addr);
-	log_post_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
+	if (rwmmio_tracepoint_enabled(rwmmio_post_write))
+		log_post_write_mmio(value, 64, addr, _THIS_IP_, _RET_IP_);
 }
 #endif
-- 
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[PATCH 6.1.y 3/3] asm-generic/io.h: Skip trace helpers if rwmmio events are disabled