Subject: Severe I/O overhead?
To: None <port-xen@netbsd.org>
From: Thor Lancelot Simon <tls@rek.tjls.com>
List: port-xen
Date: 07/14/2005 18:26:37
Both Jed and I have noticed a huge increase in latency for small I/O operations
in NetBSD/xen when compared to NetBSD/i386, even running in domain0.

One easy way to see this is to time the extraction followed by the removal
of pkgsrc with soft updates turned on.  The rm -rf takes about three times as
long in domain0 on both of our systems as it does running a "bare hardware"
kernel on the same machines.  The time isn't accounted as system time and I
have to guess that it's going to interrupt handling.

Does anyone see an obvious cause for this?  A cure?  I assume this is why
even though sequential I/O is not *that* much slower, and CPU-intensive
stuff obviously is just as fast, things like system and package builds are
so much slower under Xen than under NetBSD/i386.

-- 
 Thor Lancelot Simon	                                      tls@rek.tjls.com

"The inconsistency is startling, though admittedly, if consistency is to be
 abandoned or transcended, there is no problem."		- Noam Chomsky