linux-kernel - [RFC PATCH v2 05/10] lib: vdso: inline do

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Message-Id: <d0f8dfb26c025d3e3eee1b5f610161ca19b942df.1577111367.git.christophe.leroy@c-s.fr>
Date:   Mon, 23 Dec 2019 14:31:06 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, arnd@...db.de,
        tglx@...utronix.de, vincenzo.frascino@....com, luto@...nel.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        x86@...nel.org
Subject: [RFC PATCH v2 05/10] lib: vdso: inline do_hres()

do_hres() is called from several places, so GCC doesn't inline
it at first.

do_hres() takes a struct __kernel_timespec * parameter for
passing the result. In the 32 bits case, this parameter corresponds
to a local var in the caller. In order to provide a pointer
to this structure, the caller has to put it in its stack and
do_hres() has to write the result in the stack. This is suboptimal,
especially on RISC processor like powerpc.

By making GCC inline the function, the struct __kernel_timespec
remains a local var using registers, avoiding the need to write and
read stack.

The improvement is significant on powerpc.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 lib/vdso/gettimeofday.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index 24e1ba838260..86d5b1c8796b 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -34,8 +34,8 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult)
 }
 #endif

-static int do_hres(const struct vdso_data *vd, clockid_t clk,
-		   struct __kernel_timespec *ts)
+static inline int do_hres(const struct vdso_data *vd, clockid_t clk,
+			  struct __kernel_timespec *ts)
 {
 	const struct vdso_timestamp *vdso_ts = &vd->basetime[clk];
 	u64 cycles, last, sec, ns;
-- 
2.13.3