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charset="us-ascii" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.15 Cc: "tiwai@suse.com" X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" Hi, I'm trying to optimize the dmix because I'm working with a big number of ch= annels (up to 16) and in this case the dmix has not a negligible impact on = performance. I'm working with ALSA 1.1.9. I gave my first look to the generic_mix_areas_= 16_native function (https://github.com/alsa-project/alsa-lib/blob/v1.1.9/sr= c/pcm/pcm_dmix_generic.c#L130). I would ask you if I can avoid to check, for each loop iteration, if the cu= rrent dst sample is not 0. for (;;) { sample =3D *src; if (! *dst) { *sum =3D sample; *dst =3D *src; } else { sample +=3D *sum; *sum =3D sample; if (sample > 0x7fff) sample =3D 0x7fff; else if (sample < -0x8000) sample =3D -0x8000; *dst =3D sample; } if (!--size) return; src =3D (signed short *) ((char *)src + src_step); dst =3D (signed short *) ((char *)dst + dst_step); sum =3D (signed int *) ((char *)sum + sum_step); } Could it be possible check for the first sample of the period only, as repo= rted in the code below? My assumption is that if dst[0] is 0 also dst[1] ..= . dst[period-1] will be 0, and I don't need to check every time. This is al= ready an optimization, but it could be also a starting point for other opti= mization based on my HW. But, first of all, I would ask to you if my assump= tion is right. if (! *dst) { for (;;) { sample =3D *src; *sum =3D sample; *dst =3D *src; if (!--size) return; src =3D (signed short *) ((char *)src + src_step); dst =3D (signed short *) ((char *)dst + dst_step); sum =3D (signed int *) ((char *)sum + sum_step); } } else { for (;;) { sample =3D *src; sample +=3D *sum; *sum =3D sample; if (sample > 0x7fff) sample =3D 0x7fff; else if (sample < -0x8000) sample =3D -0x8000; *dst =3D sample; if (!--size) return; src =3D (signed short *) ((char *)src + src_step); dst =3D (signed short *) ((char *)dst + dst_step); sum =3D (signed int *) ((char *)sum + sum_step); } } Thank you! Best Regards, Giuliano