[alsa-devel] snd_pcm_writei VS snd_pcm_mmap_writei
Hello,
Please tell me a) Difference between working of snd_pcm_mmap_writei and snd_pcm_writei ? b) Performance wise which is better ?
When i use gettimeofday almost profile time comes almost same for both of them.
Thanks and Regards, Irfan
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On Fri, 19 Nov 2010, Irfan Shaikh wrote:
Hello,
Please tell me a) Difference between working of snd_pcm_mmap_writei and snd_pcm_writei ? b) Performance wise which is better ?
The mmap functions does not require user space / kernel context switches.
When i use gettimeofday almost profile time comes almost same for both of them.
With current hw power, there are no major differences.
Jaroslav
----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.
Jaroslav Kysela wrote:
On Fri, 19 Nov 2010, Irfan Shaikh wrote:
Please tell me a) Difference between working of snd_pcm_mmap_writei and snd_pcm_writei ?The mmap functions does not require user space / kernel context switches.
b) Performance wise which is better ? When i use gettimeofday almost profile time comes almost same for both of them.With current hw power, there are no major differences.
Yes, the context switches have no noticeable impact on latency or throughput.
The only case where using the mmap functions makes sense is when the program generates the samples on the fly and can write them directly into the device's buffer. If, however, the samples are already in some other buffer and are to be copied into the device's buffer, then this is _exactly_ the same situation as snd_pcm_writei.
If your algorithm requires that you always use snd_pcm_mmap_writei, then you shouldn't have used mmap in the first place.
Regards, Clemens
participants (3)
-
Clemens Ladisch -
Irfan Shaikh -
Jaroslav Kysela