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linux-next/arch/x86/include/asm/timer.h
Peter Zijlstra 5dd12c2152 sched/clock, 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>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-piu203ses5y1g36bnyw2n16x@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-01-13 13:47:38 +01:00

79 lines
2.1 KiB
C

#ifndef _ASM_X86_TIMER_H
#define _ASM_X86_TIMER_H
#include <linux/init.h>
#include <linux/pm.h>
#include <linux/percpu.h>
#include <linux/interrupt.h>
#include <linux/math64.h>
#define TICK_SIZE (tick_nsec / 1000)
unsigned long long native_sched_clock(void);
extern int recalibrate_cpu_khz(void);
extern int no_timer_check;
/* Accelerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
* ns = cycles * (ns_per_sec / freq)
* ns = cycles * (10^9 / (cpu_khz * 10^3))
* ns = cycles * (10^6 / cpu_khz)
*
* Then we use scaling math (suggested by george@mvista.com) to get:
* ns = cycles * (10^6 * SC / cpu_khz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
* We can use khz divisor instead of mhz to keep a better precision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*
* In:
*
* ns = cycles * cyc2ns_scale / SC
*
* Although we may still have enough bits to store the value of ns,
* in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
* leading to an incorrect result.
*
* To avoid this, we can decompose 'cycles' into quotient and remainder
* of division by SC. Then,
*
* ns = (quot * SC + rem) * cyc2ns_scale / SC
* = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
*
* - sqazi@google.com
*/
DECLARE_PER_CPU(unsigned long, cyc2ns);
DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns = this_cpu_read(cyc2ns_offset);
ns += mul_u64_u32_shr(cyc, this_cpu_read(cyc2ns), CYC2NS_SCALE_FACTOR);
return ns;
}
static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns;
unsigned long flags;
local_irq_save(flags);
ns = __cycles_2_ns(cyc);
local_irq_restore(flags);
return ns;
}
#endif /* _ASM_X86_TIMER_H */