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Subject[PATCH 09/15] x86: Use mul_u64_u32_shr() for native_sched_clock()
Use mul_u64_u32_shr() so that x86_64 can use a single 64x64->128 mul.

before:

0000000000000560 <native_sched_clock>:
560: 44 8b 1d 00 00 00 00 mov 0x0(%rip),%r11d # 567 <native_sched_clock+0x7>
567: 55 push %rbp
568: 48 89 e5 mov %rsp,%rbp
56b: 45 85 db test %r11d,%r11d
56e: 75 4f jne 5bf <native_sched_clock+0x5f>
570: 0f 31 rdtsc
572: 89 c0 mov %eax,%eax
574: 48 c1 e2 20 shl $0x20,%rdx
578: 48 c7 c1 00 00 00 00 mov $0x0,%rcx
57f: 48 09 c2 or %rax,%rdx
582: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
589: 65 8b 04 25 00 00 00 mov %gs:0x0,%eax
590: 00
591: 48 98 cltq
593: 48 8b 34 c5 00 00 00 mov 0x0(,%rax,8),%rsi
59a: 00
59b: 48 89 d0 mov %rdx,%rax
59e: 81 e2 ff 03 00 00 and $0x3ff,%edx
5a4: 48 c1 e8 0a shr $0xa,%rax
5a8: 48 0f af 14 0e imul (%rsi,%rcx,1),%rdx
5ad: 48 0f af 04 0e imul (%rsi,%rcx,1),%rax
5b2: 5d pop %rbp
5b3: 48 03 04 3e add (%rsi,%rdi,1),%rax
5b7: 48 c1 ea 0a shr $0xa,%rdx
5bb: 48 01 d0 add %rdx,%rax
5be: c3 retq

after:

0000000000000550 <native_sched_clock>:
550: 8b 3d 00 00 00 00 mov 0x0(%rip),%edi # 556 <native_sched_clock+0x6>
556: 55 push %rbp
557: 48 89 e5 mov %rsp,%rbp
55a: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
55e: 85 ff test %edi,%edi
560: 75 2c jne 58e <native_sched_clock+0x3e>
562: 0f 31 rdtsc
564: 89 c0 mov %eax,%eax
566: 48 c1 e2 20 shl $0x20,%rdx
56a: 48 09 c2 or %rax,%rdx
56d: 65 48 8b 04 25 00 00 mov %gs:0x0,%rax
574: 00 00
576: 89 c0 mov %eax,%eax
578: 48 f7 e2 mul %rdx
57b: 65 48 8b 0c 25 00 00 mov %gs:0x0,%rcx
582: 00 00
584: c9 leaveq
585: 48 0f ac d0 0a shrd $0xa,%rdx,%rax
58a: 48 01 c8 add %rcx,%rax
58d: c3 retq

MAINLINE POST

sched_clock_stable: 1 1
(cold) sched_clock: 329841 331312
(cold) local_clock: 301773 310296
(warm) sched_clock: 38375 38247
(warm) local_clock: 100371 102713
(warm) rdtsc: 27340 27289
sched_clock_stable: 0 0
(cold) sched_clock: 382634 372706
(cold) local_clock: 396890 399275
(warm) sched_clock: 38194 38124
(warm) local_clock: 143452 148698
(warm) rdtsc: 27345 27365

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
arch/x86/include/asm/timer.h | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

--- a/arch/x86/include/asm/timer.h
+++ b/arch/x86/include/asm/timer.h
@@ -4,6 +4,7 @@
#include <linux/pm.h>
#include <linux/percpu.h>
#include <linux/interrupt.h>
+#include <linux/math64.h>

#define TICK_SIZE (tick_nsec / 1000)

@@ -57,10 +58,8 @@ DECLARE_PER_CPU(unsigned long long, cyc2

static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
- int cpu = smp_processor_id();
- unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
- ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
- (1UL << CYC2NS_SCALE_FACTOR));
+ unsigned long long ns = this_cpu_read(cyc2ns_offset);
+ ns += mul_u64_u32_shr(cyc, this_cpu_read(cyc2ns), CYC2NS_SCALE_FACTOR);
return ns;
}




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