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Message-ID: <CAOLDJO+=+hcz498KRc+95dF5y3hZdtm+3y35o2rBC9qAOF-vDg@mail.gmail.com>
Date: Mon, 7 Apr 2025 18:13:44 +0200
From: Varad Gautam <varadgautam@...gle.com>
To: linux-arch@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>, Sai Prakash Ranjan <quic_saipraka@...cinc.com>,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] asm-generic/io.h: Skip trace helpers if rwmmio events are disabled
On Sun, Mar 30, 2025 at 6:42 PM Varad Gautam <varadgautam@...gle.com> wrote:
>
> 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@...gle.com>
> Fixes: 210031971cdd ("asm-generic/io: Add logging support for MMIO accessors")
> Cc: <stable@...r.kernel.org>
Ping.
> ---
> 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 3c61c29ff6ab..a9b5da547523 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -75,6 +75,7 @@
> #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);
> @@ -91,6 +92,7 @@ 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,
> @@ -189,11 +191,13 @@ 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
> @@ -204,11 +208,13 @@ 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
> @@ -219,11 +225,13 @@ 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
> @@ -235,11 +243,13 @@ 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
> @@ -249,11 +259,13 @@ 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
>
> @@ -261,11 +273,13 @@ 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
>
> @@ -273,11 +287,13 @@ 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
>
> @@ -286,11 +302,13 @@ 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 */
> @@ -306,9 +324,11 @@ 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
> @@ -319,9 +339,11 @@ 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
> @@ -332,9 +354,11 @@ 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
> @@ -345,9 +369,11 @@ 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
> @@ -356,9 +382,11 @@ 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
>
> @@ -366,9 +394,11 @@ 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
>
> @@ -376,9 +406,11 @@ 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
>
> @@ -386,9 +418,11 @@ 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
>
> --
> 2.49.0.472.ge94155a9ec-goog
>
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