Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [RFC PATCH v3 04/12] lib: vdso: inline do_hres() and do_coarse() | Date | Mon, 13 Jan 2020 17:08:42 +0000 (UTC) |
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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: Before: gettimeofday: vdso: 1379 nsec/call clock-gettime-realtime-coarse: vdso: 868 nsec/call clock-gettime-realtime: vdso: 1511 nsec/call clock-gettime-monotonic-raw: vdso: 1576 nsec/call
After: gettimeofday: vdso: 1078 nsec/call clock-gettime-realtime-coarse: vdso: 807 nsec/call clock-gettime-realtime: vdso: 1256 nsec/call clock-gettime-monotonic-raw: vdso: 1316 nsec/call
At the same time, change the return type of do_coarse() to int, this increase readability of the if/elseif/elseif/else section in __cvdso_clock_gettime_common()
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> --- lib/vdso/gettimeofday.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-)
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 42bd8ab955fa..d75e44ba716f 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -38,8 +38,8 @@ 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 __always_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; @@ -68,8 +68,8 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk, return 0; } -static void do_coarse(const struct vdso_data *vd, clockid_t clk, - struct __kernel_timespec *ts) +static __always_inline int do_coarse(const struct vdso_data *vd, clockid_t clk, + struct __kernel_timespec *ts) { const struct vdso_timestamp *vdso_ts = &vd->basetime[clk]; u32 seq; @@ -79,6 +79,8 @@ static void do_coarse(const struct vdso_data *vd, clockid_t clk, ts->tv_sec = vdso_ts->sec; ts->tv_nsec = vdso_ts->nsec; } while (unlikely(vdso_read_retry(vd, seq))); + + return 0; } static __maybe_unused int @@ -96,15 +98,16 @@ __cvdso_clock_gettime_common(clockid_t clock, struct __kernel_timespec *ts) * clocks are handled in the VDSO directly. */ msk = 1U << clock; - if (likely(msk & VDSO_HRES)) { - return do_hres(&vd[CS_HRES_COARSE], clock, ts); - } else if (msk & VDSO_COARSE) { - do_coarse(&vd[CS_HRES_COARSE], clock, ts); - return 0; - } else if (msk & VDSO_RAW) { - return do_hres(&vd[CS_RAW], clock, ts); - } - return -1; + if (likely(msk & VDSO_HRES)) + vd += CS_HRES_COARSE; + else if (msk & VDSO_COARSE) + return do_coarse(&vd[CS_HRES_COARSE], clock, ts); + else if (msk & VDSO_RAW) + vd += CS_RAW; + else + return -1; + + return do_hres(vd, clock, ts); } static __maybe_unused int -- 2.13.3
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