 |
SDL2 Audio Callback Buffer Change |  |
|
Brian Barnes
Guest
|
|
Sam wrote:
(I changed the subject to be better) Hmmm, OK, that's definitely a change from 1.2, and it seems to still be the case for OS X and iOS version. If there's a standard, let's get it into the docs and let me know which way you guys want to do it. The core audio one (if I'm reading the code correctly) actually has this in it: while (remaining > 0) { if (this->hidden->bufferOffset >= this->hidden->bufferSize) { /* Generate the data */ SDL_memset(this->hidden->buffer, this->spec.silence, this->hidden->bufferSize); SDL_mutexP(this->mixer_lock); (*this->spec.callback)(this->spec.userdata, this->hidden->buffer, this->hidden->bufferSize); SDL_mutexV(this->mixer_lock); this->hidden->bufferOffset = 0; } Basically, whatever way it should be, you should probably get it in the docs and make all the versions do the same thing. [>] Brian |
||||||||||||
|
||||||||||||||
|
SDL2 Audio Callback Buffer Change | |
|
Sam Lantinga
|
|
Yep, thanks for the heads up. I'll pull the memset from those drivers.
Cheers! On Wed, Jul 4, 2012 at 12:53 PM, Brian Barnes wrote:
|
||||||||||||||
|
||||||||||||||||
|
SDL2 Audio Callback Buffer Change | |
|
Sam Lantinga
|
|
Done!
On Thu, Jul 5, 2012 at 12:03 PM, Sam Lantinga wrote:
|
||||||||||||||||
|
||||||||||||||||||
|
SDL2 Audio Callback Buffer Change | |
|
Forest Hale
Guest
|
|
I will note that in my game engines I regularly use memset before writing streaming data to intentionally fill the cache lines, with a small but measurable performance benefit on x86 despite the
redundancy of the act itself. Never really figured out why it helps but it does in my experience, I can only assume that my stream writing code is failing to satisfy the write-combine logic in some way. I have confirmed a performance gain from memset before writing on everything I've ever tried it on - sound data copies out of mixer buffers, skeletal animation of model vertices, and so on... But I do not have sufficient experience with other architectures to say whether memsetting first is a win or loss on other CPU architectures, just that on x86 it seems to help. On 07/05/2012 09:03 AM, Sam Lantinga wrote:
-- LordHavoc Author of DarkPlaces Quake1 engine - http://icculus.org/twilight/darkplaces Co-designer of Nexuiz - http://alientrap.org/nexuiz "War does not prove who is right, it proves who is left." - Unknown "Any sufficiently advanced technology is indistinguishable from a rigged demo." - James Klass "A game is a series of interesting choices." - Sid Meier _______________________________________________ SDL mailing list http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org |
||||||||||||||
|
||||||||||||||||
|
SDL2 Audio Callback Buffer Change | |
|
Vance, Michael
Guest
|
|
On many architectures memset benefits from hardware support from instructions like dcbz on the PPC (which is essentially a combined prefetch or cache block zero). If you find optimizations like this interesting you may also want to explore usage of the restrict keyword.
m.
SDL mailing list http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org |
||||||||||||||||||||||||
|
||||||||||||||||||||||||||
|
SDL2 Audio Callback Buffer Change | |
|
Sam Lantinga
|
|
The memset implementation is probably using SIMD with a prefetch instruction. You might be able to get the same benefit by inlining that asm yourself. There are some examples of this in the SDL blitter code. :)
On Thu, Jul 5, 2012 at 12:26 PM, Forest Hale wrote:
|
||||||||||||||||||||
|
||||||||||||||||||||||