From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
nathanl@linux.ibm.com, arnd@arndb.de, tglx@linutronix.de,
vincenzo.frascino@arm.com, luto@kernel.org
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
x86@kernel.org
Subject: [RFC PATCH v4 11/11] powerpc/32: provide vdso_shift_ns()
Date: Thu, 16 Jan 2020 17:58:35 +0000 (UTC) [thread overview]
Message-ID: <29f979e09c84c95f08fcd15386576e32c546d04b.1579196675.git.christophe.leroy@c-s.fr> (raw)
In-Reply-To: <cover.1579196675.git.christophe.leroy@c-s.fr>
The generic x >> s gives the following result:
18: 35 25 ff e0 addic. r9,r5,-32
1c: 41 80 00 10 blt 2c <shift+0x14>
20: 7c 64 4c 30 srw r4,r3,r9
24: 38 60 00 00 li r3,0
...
2c: 54 69 08 3c rlwinm r9,r3,1,0,30
30: 21 45 00 1f subfic r10,r5,31
34: 7c 84 2c 30 srw r4,r4,r5
38: 7d 29 50 30 slw r9,r9,r10
3c: 7c 63 2c 30 srw r3,r3,r5
40: 7d 24 23 78 or r4,r9,r4
In our case the shift is always < 32. In addition, the upper 32 bits
of the result are likely nul. Lets GCC know it, it also optimises the
following calculations.
With the patch, we get:
0: 21 25 00 20 subfic r9,r5,32
4: 7c 69 48 30 slw r9,r3,r9
8: 7c 84 2c 30 srw r4,r4,r5
c: 7d 24 23 78 or r4,r9,r4
10: 7c 63 2c 30 srw r3,r3,r5
Performance before the patch:
clock-gettime-realtime: vdso: 1033 nsec/call
After the patch:
clock-gettime-realtime: vdso: 941 nsec/call
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/include/asm/vdso/gettimeofday.h | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/arch/powerpc/include/asm/vdso/gettimeofday.h b/arch/powerpc/include/asm/vdso/gettimeofday.h
index 74b6eef8fbe9..716a137ab166 100644
--- a/arch/powerpc/include/asm/vdso/gettimeofday.h
+++ b/arch/powerpc/include/asm/vdso/gettimeofday.h
@@ -95,6 +95,23 @@ static __always_inline u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 m
}
#define vdso_calc_delta vdso_calc_delta
+#ifndef __powerpc64__
+static __always_inline u64 vdso_shift_ns(u64 ns, unsigned long shift)
+{
+ u32 hi = ns >> 32;
+ u32 lo = ns;
+
+ lo = (lo >> shift) | (hi << (32 - shift));
+ hi >>= shift;
+
+ if (likely(hi == 0))
+ return lo;
+
+ return ((u64)hi << 32) | lo;
+}
+#define vdso_shift_ns vdso_shift_ns
+#endif
+
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_VDSO_GETTIMEOFDAY_H */
--
2.13.3
next prev parent reply other threads:[~2020-01-16 17:58 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 17:58 [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 01/11] powerpc/64: Don't provide time functions in compat VDSO32 Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 02/11] powerpc/vdso: Switch VDSO to generic C implementation Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 03/11] lib: vdso: only read hrtimer_res when needed in __cvdso_clock_getres() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 04/11] powerpc/vdso: simplify __get_datapage() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 05/11] lib: vdso: allow arches to provide vdso data pointer Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 06/11] powerpc/vdso: provide inline alternative to __get_datapage() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 07/11] powerpc/vdso: provide vdso data pointer from the ASM caller Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 08/11] lib: vdso: allow fixed clock mode Christophe Leroy
2020-01-16 20:13 ` Thomas Gleixner
2020-01-16 20:19 ` Andy Lutomirski
2020-01-16 21:07 ` Thomas Gleixner
2020-01-16 17:58 ` [RFC PATCH v4 09/11] powerpc/vdso: override __arch_vdso_capable() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation Christophe Leroy
2020-01-16 19:47 ` Andy Lutomirski
2020-01-16 19:57 ` Thomas Gleixner
2020-01-16 20:20 ` Andy Lutomirski
2020-01-29 7:14 ` Thomas Gleixner
2020-01-29 7:26 ` Christophe Leroy
2020-01-16 17:58 ` Christophe Leroy [this message]
2020-01-17 8:58 ` [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation Segher Boessenkool
2020-01-17 9:26 ` Christophe Leroy
2020-01-20 14:56 ` Christophe Leroy
2020-01-20 15:19 ` Segher Boessenkool
2020-01-20 17:08 ` Christophe Leroy
2020-01-20 17:27 ` Segher Boessenkool
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