Re: Poor Xinerama Performance
The most 'interesting' piece of evidence is that on occasion top shows the 'si' field field of the CPU summary in the area of 80 - 90%. Presumably 'si' is softirq - it doesn't seem to be mentioneed in top's man page.
I very much doubt that it should ever reach this value on any running system. It seems most unlikely to me that this is due to PCI bus bandwidth limitations or not using OpenGL etc etc.
I read another thread about real time Linux, SMP issues. It is mentioned that some of the glue code is using semaphores in interrupt context. As the poster says, this is wrong and probably wrong on any OS. I'm not saying that this is neccessarily the cause of my performance issues, but given the high 'si' values it may be relevent. I will spend a little time looking at the code, understanging the patches etc.
Incidently I tried apci=off kernel boot option. It possibly made things slightly worse - certainly no better.