On 04.09.2015 08:49, Alexey Klimov wrote:
> Since evt structure is embedded in per-CPU mevt structure it's
> definitely faster to use container_of() to get access to mevt
> if we have evt (for example as incoming function argument) instead
> of more expensive approach with this_cpu_ptr(&percpu_mct_tick).
> this_cpu_ptr() on per-CPU mevt structure leads to access to cp15
> to get cpu id and arithmetic operations.
> Container_of() is cheaper since it's just one asm instruction.
> This should work if used evt pointer is correct and owned by
> local mevt structure.
>
> For example, before this patch set_state_shutdown() looks like:
>
> 4a4: e92d4010 push {r4, lr}
> 4a8: e3004000 movw r4, #0
> 4ac: ebfffffe bl 0 <debug_smp_processor_id>
> 4b0: e3003000 movw r3, #0
> 4b4: e3404000 movt r4, #0
> 4b8: e3403000 movt r3, #0
> 4bc: e7933100 ldr r3, [r3, r0, lsl #2]
> 4c0: e0844003 add r4, r4, r3
> 4c4: e59400c0 ldr r0, [r4, #192] ; 0xc0
> 4c8: ebffffd4 bl 420 <exynos4_mct_tick_stop.isra.1>
> 4cc: e3a00000 mov r0, #0
> 4d0: e8bd8010 pop {r4, pc}
>
> With this patch:
>
> 4a4: e92d4010 push {r4, lr}
> 4a8: e59000c0 ldr r0, [r0, #192] ; 0xc0
> 4ac: ebffffdb bl 420 <exynos4_mct_tick_stop.isra.1>
> 4b0: e3a00000 mov r0, #0
> 4b4: e8bd8010 pop {r4, pc}
>
> Also, for me size of exynos_mct.o decreased from 84588 bytes
> to 83956.
>
> Signed-off-by: Alexey Klimov <alexey.kli...@linaro.org>
> ---
> drivers/clocksource/exynos_mct.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
Looks good and sensible. Why you called this RFC? You are not sure if
this is correct?
One minor nit-pick below, but I am fine without it anyway:
Reviewed-by: Krzysztof Kozlowski <k.kozlow...@samsung.com>
>
> diff --git a/drivers/clocksource/exynos_mct.c
> b/drivers/clocksource/exynos_mct.c
> index 029f96a..ff44082 100644
> --- a/drivers/clocksource/exynos_mct.c
> +++ b/drivers/clocksource/exynos_mct.c
> @@ -382,24 +382,28 @@ static void exynos4_mct_tick_start(unsigned long cycles,
> static int exynos4_tick_set_next_event(unsigned long cycles,
> struct clock_event_device *evt)
> {
> - struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
> + struct mct_clock_event_device *mevt;
>
> + mevt = container_of(evt, struct mct_clock_event_device, evt);
> exynos4_mct_tick_start(cycles, mevt);
> -
Actually I would prefer leaving the empty line here and add such in
function below. For me the code is more readable with
ending return separated by one line.
Best regards,
Krzysztof
> return 0;
> }
>
> static int set_state_shutdown(struct clock_event_device *evt)
> {
> - exynos4_mct_tick_stop(this_cpu_ptr(&percpu_mct_tick));
> + struct mct_clock_event_device *mevt;
> +
> + mevt = container_of(evt, struct mct_clock_event_device, evt);
> + exynos4_mct_tick_stop(mevt);
> return 0;
> }
>
> static int set_state_periodic(struct clock_event_device *evt)
> {
> - struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
> + struct mct_clock_event_device *mevt;
> unsigned long cycles_per_jiffy;
>
> + mevt = container_of(evt, struct mct_clock_event_device, evt);
> cycles_per_jiffy = (((unsigned long long)NSEC_PER_SEC / HZ * evt->mult)
> >> evt->shift);
> exynos4_mct_tick_stop(mevt);
>
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