Messages in this thread Patch in this message | | | Subject | Re: [RFC PATCH v2 05/10] lib: vdso: inline do_hres() | From | Christophe Leroy <> | Date | Sat, 11 Jan 2020 09:06:49 +0000 |
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On 01/10/2020 09:07 PM, Thomas Gleixner wrote: > Arnd Bergmann <arnd@arndb.de> writes: >> On Mon, Dec 23, 2019 at 3:31 PM Christophe Leroy >> <christophe.leroy@c-s.fr> wrote: >>> >>> 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> >> >> Good idea, I can see how this ends up being an improvement >> for most of the callers. >> >> Acked-by: Arnd Bergmann <arnd@arndb.de> > > https://lore.kernel.org/r/20191112012724.250792-3-dima@arista.com > > On the way to be applied. >
Oh nice, I get even better result with the way it is done by Dmitry compared to my own first patch.
On an mpc8xx at 132Mhz (32bits powerpc), before the patch I have gettimeofday: vdso: 1256 nsec/call clock-gettime-monotonic-raw: vdso: 1449 nsec/call clock-gettime-monotonic-coarse: vdso: 768 nsec/call clock-gettime-monotonic: vdso: 1390 nsec/call
With the patch I have: gettimeofday: vdso: 947 nsec/call clock-gettime-monotonic-raw: vdso: 1156 nsec/call clock-gettime-monotonic-coarse: vdso: 638 nsec/call clock-gettime-monotonic: vdso: 1094 nsec/call
So that's a 20-25% improvement.
I modified it slightly as follows:
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 9e474d54814f..b793f211bca8 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -37,8 +37,8 @@ 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; @@ -67,8 +67,8 @@ 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; @@ -78,6 +78,8 @@ 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 @@ -95,15 +97,16 @@ __cvdso_clock_gettime_common(const struct vdso_data *vd, clockid_t clock, * 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 --- Christophe
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