Re: Deterministic behavior for TTY serial

On Thu, May 03, 2012 at 05:28:47PM +0200, Ivo Sieben wrote:

Hi,

quoted

The PREEMPT_RT uses mutexes for "normal" spin locks that do not
disable interrupts...
I'll try to use raw spinlocks in this code section and for the tty flip buffer
See if that can solve my problem.

If you have other ideas... let me know!

Regards,
Ivo

I've changed some small things to the tty layer (see my other 3 RFC
patches I've send).
Performance increased with my loopback stress test:
- Old situation: average read call last for 50us, with peaks up to 230 us
- New situation: average read call still 50us, peak up to 60 us
- Write was stable in both situations: average of 90 us, peak up to 100 us

Only the very first read & write took extra time (128 us for read, 143
for write)
I'm still investigating that...

Feedback is very appreciated.

Why are raw spinlocks "faster" here?  I like the end-result of what you
have accomplished, but I had some questions on your patches, care to
answer them?

thanks,

greg k-h