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SubjectRe: [RFC PATCH] clocksource: exynos_mct: use container_of() instead of this_cpu_ptr()
On 09/04/2015 01:49 AM, 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.klimov@linaro.org>
> ---

Despite the RFC I applied the patch as it seems simple enough and it has
been reviewed by Krzysztof.

-- Daniel


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