Command Buffer

[Andreas Ericsson]

Ruiz, Francisco wrote:
> Greetings,
> 
> I was hoping someone could elaborate more on the command buffer, and
> what the significance is of going from 4k to 32k.
> 

The size of IPC pipes (FIFO's) is specified in the kernel of your OS. 
You can set it to whatever you like, but you might run into weird things 
depending on your system type. For instance, on most 32-bit 
architectures the kernel allocates memory in blocks of 4096 bytes, so 
that's the size of a FIFO. If you make the FIFO bigger, the kernel needs 
to do exception handling when you write anything larger than that to the 
pipe, and if it doesn't you'll end up with either a message that get's 
truncated anyway or something undefined.

What you WILL get is performance that's about 1/3 of what you'd get if 
you don't meddle with it.

For reference, Linux users have reported this to work splendidly on 
kernels since 2.4.20, although the code suggests that FIFO handling 
changed quite a bit somewhere in 2.3 and there-about.

> Thanks! 
> 
> 
> 
> 
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-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Lead Developer


-------------------------------------------------------
SF.Net email is Sponsored by the Better Software Conference & EXPO
September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
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