Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [PATCH v8 7/8] lib/vdso: force inlining of __cvdso_clock_gettime_common() | Date | Tue, 28 Apr 2020 13:16:53 +0000 (UTC) |
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When adding gettime64() to a 32 bit architecture (namely powerpc/32) it has been noticed that GCC doesn't inline anymore __cvdso_clock_gettime_common() because it is called twice (Once by __cvdso_clock_gettime() and once by __cvdso_clock_gettime32).
This has the effect of seriously degrading the performance:
Before the implementation of gettime64(), gettime() runs in:
clock-gettime-monotonic-raw: vdso: 1003 nsec/call clock-gettime-monotonic-coarse: vdso: 592 nsec/call clock-gettime-monotonic: vdso: 942 nsec/call
When adding a gettime64() entry point, the standard gettime() performance is degraded by 30% to 50%:
clock-gettime-monotonic-raw: vdso: 1300 nsec/call clock-gettime-monotonic-coarse: vdso: 900 nsec/call clock-gettime-monotonic: vdso: 1232 nsec/call
Adding __always_inline() to __cvdso_clock_gettime_common() regains the original performance.
In terms of code size, the inlining increases the code size by only 176 bytes. This is in the noise for a kernel image.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> --- lib/vdso/gettimeofday.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index a2909af4b924..7938d3c4901d 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -210,7 +210,7 @@ static __always_inline int do_coarse(const struct vdso_data *vd, clockid_t clk, return 0; } -static __maybe_unused int +static __always_inline int __cvdso_clock_gettime_common(const struct vdso_data *vd, clockid_t clock, struct __kernel_timespec *ts) { -- 2.25.0
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