On Fri, Oct 17, 2008 at 11:39:40AM +0100, Daniel P. Berrange wrote:
Looking at the libvirtd objects with pfunct I knoticed that the method remoteDispatchClientRequest in remote.c was unusually large
size: 11497, variables: 169, inline expansions: 159 (5144 bytes)
Listing variables present its clear why - for every RPC call, we have a pair of local variables declared for the structs for the reply and response. Following by a memset() call for every single one.
Any single call to this method only processes one RPC call, so I figured we could collapse all these variables down into a single pair by using a union for all args, and a union for all replies.
This patch does just that with the result that the method changes to:
/* size: 1386, variables: 10, inline expansions: 4 (89 bytes) */
If you want to see details list of variables before and after results then run
$ pfunct -f remoteDispatchClientRequest libvirtd-remote.o
NB pfunct is in the 'dwarves' RPM, along with some other interesting tools like 'pahole'
In doing this I noticed that the dispatch function is O(n) on the number of RPC calls we have defined. This isn't a serious bottleneck since 'n' isn't very large, but while doing the refactoring for the union stuf, it was easy enough to also change it to declare an array of all the dispatch methods, which could simply be indexed on the RPC call number. This changes it to O(1) time to dispatch.
The patch tends to generate headaches, and I still can't grok perl, but what I recognized looks fine, and the principles sounds good. Daniel -- Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/ daniel@veillard.com | Rpmfind RPM search engine http://rpmfind.net/ http://veillard.com/ | virtualization library http://libvirt.org/