[Xen-devel] Interrupt Coalescence

[Håvard Bjerke <havarbj@xxxxxxxxxxx>]

I've found that Interrupt Coalescence (IC) has a detrimental effect on some 
benchmarks with the e1000 driver. So I tried disabling it with the argument 
"InterruptThrottleRate=0,0".

This had the wanted effect in native linux, ie. full speed, 116 MB/s. However, 
in Xen0, disabling IC has the effect of severely reducing bandwidth down to 
around 1 MB/s.

Turning of IC has the effect that an interrupt is generated from the NIC for 
each received or sent MTU (1500 bytes). On a gigabit network this means that an 
interrupt may be generated, according to 
[http://www.pam2004.org/papers/265.pdf], every 12 us.

I looked at #interrupts generated with and without IC, and they are ~ 1100 and 
~ 400 respectively when sending a 2 MB message with ttcp.

So I'm trying to explain what's happening. Is Xen slower in handling the 
interrupts than native? The CPU is an Intel P4 @ 3400 MHz. Does it need more 
than 12 us to do a context switch when using Xen?


Håvard


-------------------------------------------------------
This SF.Net email is sponsored by:
Sybase ASE Linux Express Edition - download now for FREE
LinuxWorld Reader's Choice Award Winner for best database on Linux.
http://ads.osdn.com/?ad_idU88&alloc_id065&op=click
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel