Re: [RFC PATCH v2 05/10] lib: vdso: inline do_hres()
On 01/10/2020 09:07 PM, Thomas Gleixner wrote:
Arnd Bergmann writes:
On Mon, Dec 23, 2019 at 3:31 PM Christophe Leroy
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
Good idea, I can see how this ends up being an improvement
for most of the callers.
Acked-by: Arnd Bergmann
https://lore.kernel.org/r/20191112012724.250792-3-d...@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 = >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 = >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([CS_HRES_COARSE], clock, ts);
- } else if (msk & VDSO_COARSE) {
- do_coarse([CS_HRES_COARSE], clock, ts);
- return 0;
- } else if (msk & VDSO_RAW) {
- return do_hres([CS_RAW], clock, ts);
- }
- return -1;
+ if (likely(msk & VDSO_HRES))
+ vd += CS_HRES_COARSE;
+ else if (msk & VDSO_COARSE)
+ return do_coarse([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
Re: [RFC PATCH v2 05/10] lib: vdso: inline do_hres()
Arnd Bergmann writes: > On Mon, Dec 23, 2019 at 3:31 PM Christophe Leroy > 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 > > Good idea, I can see how this ends up being an improvement > for most of the callers. > > Acked-by: Arnd Bergmann https://lore.kernel.org/r/20191112012724.250792-3-d...@arista.com On the way to be applied. Thanks, tglx
Re: [RFC PATCH v2 05/10] lib: vdso: inline do_hres()
On Mon, Dec 23, 2019 at 3:31 PM Christophe Leroy 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 Good idea, I can see how this ends up being an improvement for most of the callers. Acked-by: Arnd Bergmann
Re: [RFC PATCH v2 05/10] lib: vdso: inline do_hres()
On Mon, Dec 23, 2019 at 6:31 AM Christophe Leroy 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. I'm okay with it, mainly because I don't expect many workloads to have more than one copy of the code hot at the same time.
[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
---
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 = >basetime[clk];
u64 cycles, last, sec, ns;
--
2.13.3
