Re: experiences beyond 4 GB RAM with 2.4.22

[Pavel Machek <pavel@suse.cz>]

Hi!

> > and memory remappings. By considering the top part of RAM as swap,
> > you'll force the important stuff into the more easily accessable
> > RAM (Compare to fastram as it was called on the Amiga!). 
> 
> You are misunderstanding the problem. You don't use bounce buffers just
> because the page happens to reside in high memory, it is only used if
> the hardware cannot DMA to it. And that is exactly the problem here with
> the 3ware adapter, it cannot dma to > 4GB. So in a 6GB setup (with
> potentially 5G of highmem), only the last 2G requires bouncing.
> 
> To answer one of the other questions regarding slowdown - it can be
> nastier than 2x, remember that for reads the copy back happens inside
> the interrupt handler... It would also be interesting to note (with

Ouch, I guess I see. If big part of time is spent in interrupt
copying data, network is going to loose packets and perform
awfully. Could he run some interrupt latency tester?

Perhaps we are copying way too much in one chunk, therefore starving
network?
Heh, old ide disk in PIO mode should allow that 6GB machine
to perform better...
At least you don't loose packets during PIO reads...
				Pavel
-- 
				Pavel
Written on sharp zaurus, because my Velo1 broke. If you have Velo you don't need...