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Subject[RFC PATCH v2 05/10] lib: vdso: inline do_hres()
Date
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@c-s.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
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