RE: [Xen-devel] Code size vs. linux source code compatibility in the hypervisor - Neugebauer, Rolf - com.xensource.lists.xen-devel

3 messages in com.xensource.lists.xen-develRE: [Xen-devel] Code size vs. linux s...

From	Sent On	Attachments
Tobias Hunger	29 Jan 2005 03:31
Neugebauer, Rolf	29 Jan 2005 04:24
Tobias Hunger	29 Jan 2005 06:32

Subject:	RE: [Xen-devel] Code size vs. linux source code compatibility in the hypervisor
From:	Neugebauer, Rolf (rolf...@intel.com)
Date:	01/29/2005 04:24:37 AM
List:	com.xensource.lists.xen-devel

As part of the next release we plan to move most of the platform init code into dom0. This includes PCI & IO-APIC setup etc for which we currently need the ACPI parts. So hopefully most of the unnecessary code you identified and probably more will disappear. rolf

-----Original Message----- From: xen-...@lists.sourceforge.net [mailto:xen-devel- adm...@lists.sourceforge.net] On Behalf Of Tobias Hunger Sent: 29 January 2005 11:32 To: xen-...@lists.sourceforge.net Subject: [Xen-devel] Code size vs. linux source code compatibility in the hypervisor

Hello there!

I recently spend some time trying to better understand the hypervisor part of xen and decided to dive into the code in the xen subdirectory. David A. Wheeler's 'SLOCCount' reports about 53k lines of C code there.

My first impression was that much of the code is in fact unused by Xen and mostly there, because it was salvaged from the Linux kernel. To aid my understanding of Xen I started to trim down on macros and functions. I was surprised to be able to actually remove about 8k lines of code and 1.5k macro definitions from the ACPI part! Xen still builds and runs for me:-) Since the compiler will optimize out unused code this reduction is not reflected in the compiled size of the hypervisor (mine is identical in size to the one build from yesterdays unstable tarball).

My question is: What is the stance of the core team on the issue of code size vs. linux source code compatibility? The less code the easier it is for others to get into the project, while keeping the complete linux code around might make moving new code over to xen easier. Are you interested in patches to remove unused code? Mine currently removes almost all the header files in include/acpi...

What do you think about #if 0 in code? I personally hate that: There is version tracking, so there is no reason to keep old code visible that way. What about all those "#ifdef CONFIG_FOO" lines from the linux kernel? Currently xen is rather fixed in the configuration it supports and uses. Is that a feature of xen (then those #ifdefs can go IMHO) or supposed to change over time?

As you might have noticed I have not used C too much for the last couple of years and never was a fan of cpp in the first place:-) This code rewriting all over the place keeps knocking me out of the flow of understanding what is happening.

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