On Tue, Jul 28, 2015 at 03:21:03PM +0200, Peter Zijlstra wrote:
> Because of the static_key restrictions we had to take an unconditional
> jump for the most likely case, causing $I bloat.
>
> Rewrite to use the new primitives.
>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> arch/x86/kernel/tsc.c | 22 ++++++++++------------
> 1 file changed, 10 insertions(+), 12 deletions(-)
>
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -38,7 +38,7 @@ static int __read_mostly tsc_unstable;
> erroneous rdtsc usage on !cpu_has_tsc processors */
> static int __read_mostly tsc_disabled = -1;
>
> -static struct static_key __use_tsc = STATIC_KEY_INIT;
> +static DEFINE_STATIC_KEY_FALSE(__use_tsc);
>
> int tsc_clocksource_reliable;
>
> @@ -274,7 +274,12 @@ static void set_cyc2ns_scale(unsigned lo
> */
> u64 native_sched_clock(void)
> {
> - u64 tsc_now;
> + if (static_branch_likely(&__use_tsc)) {
> + u64 tsc_now = rdtsc();
> +
> + /* return the value in ns */
> + return cycles_2_ns(tsc_now);
> + }
Hallelujah, this asm finally looks good:
native_sched_clock:
pushq %rbp #
movq %rsp, %rbp #,
andq $-16, %rsp #,
#APP
# 36 "./arch/x86/include/asm/jump_label.h" 1
1:.byte 0xe9
.long .L121 - 2f #
2:
.pushsection __jump_table, "aw"
.balign 8
.quad 1b, .L121, __use_tsc+1 #,
.popsection
# 0 "" 2
# 124 "./arch/x86/include/asm/msr.h" 1
rdtsc
# 0 "" 2
#NO_APP
...
leave
ret
.L121:
imulq $1000000, jiffies_64(%rip), %rdx #, jiffies_64, D.28480
movabsq $-4294667296000000, %rax #, tmp135
leave
addq %rdx, %rax # D.28480, D.28480
ret
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
