[FFmpeg-devel] [PATCH]Two patches from github

[Benoit Fouet]

Hi,


On 15/05/2017 12:40, Carl Eugen Hoyos wrote:
>
> 0002-avutil-Use-_SC_NPROCESSORS_CONF.patch
>
>
> From 42766f345dbf398716c6fd9072f072f5fa91c940 Mon Sep 17 00:00:00 2001
> From: Steve Kondik <steve at cyngn.com>
> Date: Tue, 16 Dec 2014 01:37:57 -0800
> Subject: [PATCH 2/2] avutil: Use _SC_NPROCESSORS_CONF
>
>  * On most Android devices, CPUs can appear and disappear due to hotplug
>    or CPU cluster management. Use the total number of CPUs instead so
>    that multithreaded decoding is properly optimized.

I'm not convinced the patch below fixes the issue described above.
The idea is to optimize the number of threads given the number of usable
CPUs.
If a user of libav* wants to make sure they use the right number, they
should make sure that the CPUs are woken up prior to calling this.
There are ways to force the system's power management to make sure that
the number of online CPUs is maximized, and, IMHO, that should be used
instead of returning the total number of CPUs on the platform.

> Change-Id: I1cbf000a1bda7b3abf0a84e971e752f176857385
> ---
>  libavutil/cpu.c |    2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/libavutil/cpu.c b/libavutil/cpu.c
> index 16e0c92..ab0965b 100644
> --- a/libavutil/cpu.c
> +++ b/libavutil/cpu.c
> @@ -282,6 +282,8 @@ int av_cpu_count(void)
>  
>      if (sysctl(mib, 2, &nb_cpus, &len, NULL, 0) == -1)
>          nb_cpus = 0;
> +#elif defined(__ANDROID__) && HAVE_SYSCONF && defined(_SC_NPROCESSORS_CONF)
> +    nb_cpus = sysconf(_SC_NPROCESSORS_CONF);
>  #elif HAVE_SYSCONF && defined(_SC_NPROC_ONLN)
>      nb_cpus = sysconf(_SC_NPROC_ONLN);
>  #elif HAVE_SYSCONF && defined(_SC_NPROCESSORS_ONLN)
> -- 1.7.10.4

-- 
Ben