kde.git is now online

I received the DVD from Chris Lee with a test conversion of KDE's Subversion repository to git.

I have uploaded it to:

http://userweb.kernel.org/~hpa/kdegit/

It's available both as a tarball and as an expanded tree.

	-hpa

P.S. I still want Kcharselect to display the Unicode names of the characters.

On Thu, 5 Apr 2007, H. Peter Anvin wrote:

Thanks. Am downloading it right now ("0% 146.99kB/s" - it will take quite some time ;)

		Linus

On Thu, 5 Apr 2007, Linus Torvalds wrote:

I'm downloading it too (794.3 KB/s).

Nicolas

On Thu, 5 Apr 2007, Nicolas Pitre wrote:

OK this is a really nice test repo. I have only 1 GB of ram, and although basic operations appear to work just fine, this data set shows its weight in some ways.

For example I think there might be ways to improve the pack mmap windowing, or git-fsck's IO patterns. For example, git-fsck --full spend 96% of the time waiting for IO completion and only 4% actually performing some work according to top. At that rate that makes fsck --full rather unusable on this repo. Without --full then fsck completes in less than 2 seconds.

Nicolas

On Thu, 5 Apr 2007, Nicolas Pitre wrote:

Without "--full", it doesn't actually really do anything much, since it will basically ignore objects that are in the pack.

With --full, there are certainly things that we could improve upon. We 
currently tend to walk things a few times for pack contents: 
 - first we do the SHA1 of the full pack
 - then we go back, and unpack and fsck each entry in the pack.

So if the pack-file is too big to fit in memory, we'll basically always read it at least twice (and that's ignoring the fact that delta lookup will obviously seek back and forth, which makes access patterns worse).

On the other hand, there's a perfectly good reason why we don't actually fsck pack-files by default. They're "stable storage". You don't normally need to. So I'd not worry too much about fsck performance. I suspect you'll find that with 1GB or RAM you'll have other performance problems that are more pressing ("git clone" comes to mind ;)

Me, I'm just 53% done with the download, so I probably won't be looking at this today ;)

			Linus

On Thu, 5 Apr 2007, Linus Torvalds wrote:

Well.... still it certainly can be helped a bit. I wouldn't mind it spending half an hour of CPU if it needs to. But I just interrupted it with ^C with the following result so far:

real 75m44.374s user 2m5.318s sys 0m54.059s

(I should have used /usr/bin/time to see the number of page faults).

Well... same issue actually. git-pack-objects spent about 40 secs firmly at 100% CPU usage counting objects.

Then it got stuck on:

	remote: Done counting 4111366 objects.

again spending 3% CPU and the rest waiting for IO with the disk definitely trashing. It didn't allocate more than 47% of memory during that phase which lasted a few minutes.

Then, the "Indexing 4111366 objects." message appeared and CPU usage went up to 6% CPU with 67% memory for pack-objects and 30% CPU and 7% memory for index-pack while the rest was spent waiting for IO. This also took maybe two minutes.

And now it reached the "Resolving 3305158 deltas." phase with only index-pack on the radar with approx 10% CPU and 19% memory, and the rest of the time waiting for IO again.

It has been probably half an our now and the thing is at:

	  21% (710502/3305158) done

So it will work and eventually complete. And the good news is that the worst part performance wise is on the client side. But it looks like we're definitely trashing the kernel buffer cache.

Nicolas

On Thu, 5 Apr 2007, Nicolas Pitre wrote:

Well, the thing is, this is "normal", and doesn't really have a lot to do with git.

If the actual working set is larger than available memory, ~5% CPU time is actually pretty good.

The only way to improve on it is to try to make the working set smaller. Sadly, that's often a really difficult thing to do ;(

Well, I seriously doubt it's the "same issue" except in the sense that yes, if you work with all objects, you are going to have a big working set.

Note that "working set" is different from "memory footprint". If you have good locality, the working set can be a *lot* smaller than the memory footprint, and that tends to be the best/only way to improve the working set: trying to not jump back-and-forth between different things.

One example of that kind of shrinkage of the working set was Junios commit 57584d9eddc3482c5db0308203b9df50dc62109c to "git blame": by comparing the *pointers* rather than what they pointed to, you avoid having to follow the pointer all the way down.

However, doing that in general tends to be very difficult. We use hashes extensively (not just the obvious SHA1 hashes, but the object lookup itself is based on hash tables etc), and while they are nice and fast O(1) when you have enough memory, they do tend to spread things out so that you are using your memory potentially very sparsely, which is the last thing you want to do if you are paging.

Side note: I finally got the thing downloaded, and so I did a

	git checkout -f

and the trace is pretty horrid. It looks something like this:

	...
	lstat("kdeaccessibility/IconThemes/mono/scalable/apps/kimagemapeditor.svgz", 0x7fff6f8d29f0) = -1 ENOENT (No such file or directory)
	mkdir("kdeaccessibility", 0777)         = -1 EEXIST (File exists)
	unlink("kdeaccessibility")              = -1 EISDIR (Is a directory)
	stat("kdeaccessibility", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
	mkdir("kdeaccessibility/IconThemes", 0777) = -1 EEXIST (File exists)
	unlink("kdeaccessibility/IconThemes")   = -1 EISDIR (Is a directory)
	stat("kdeaccessibility/IconThemes", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
	mkdir("kdeaccessibility/IconThemes/mono", 0777) = -1 EEXIST (File exists)
	unlink("kdeaccessibility/IconThemes/mono") = -1 EISDIR (Is a directory)
	stat("kdeaccessibility/IconThemes/mono", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
	mkdir("kdeaccessibility/IconThemes/mono/scalable", 0777) = -1 EEXIST (File exists)
	unlink("kdeaccessibility/IconThemes/mono/scalable") = -1 EISDIR (Is a directory)
	stat("kdeaccessibility/IconThemes/mono/scalable", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
	mkdir("kdeaccessibility/IconThemes/mono/scalable/apps", 0777) = -1 EEXIST (File exists)
	unlink("kdeaccessibility/IconThemes/mono/scalable/apps") = -1 EISDIR (Is a directory)
	stat("kdeaccessibility/IconThemes/mono/scalable/apps", {st_mode=S_IFDIR|0775, st_size=12288, ...}) = 0
	open("kdeaccessibility/IconThemes/mono/scalable/apps/kimagemapeditor.svgz", O_WRONLY|O_CREAT|O_EXCL, 0666) = 5
	write(5, "\37\213\10\10\205\3\263A\0\3kimagemapeditor.svg\0\344Z"..., 10112) = 10112
	close(5)                                = 0
	lstat("kdeaccessibility/IconThemes/mono/scalable/apps/kimagemapeditor.svgz", {st_mode=S_IFREG|0664, st_size=10112, ...}) = 0
	...

and that repeats for every single file. There's 233,902 of them. Oops.

On the other hand, we do certain things pretty well. A "git diff", with enough memory, takes 0.65s. That's just over *half*a*second* for 233 *thousand* files. I'd want to have tons of memory to work with this repository, but if I did, I'd still think git is the best thing since sliced bread.

And doing ops like "git blame" on some random file I looked at was actually instantaneous. I probably happened to pick a new file just by luck, but still.. Most things definitely work pretty damn well.

(Update: I did a

	git log --raw -r |
		grep '^:100644.*M' |
		cut -f2 |
		sort |
		uniq -c |
		sort -n

to see the file that was updated the most, to get some kind of worst-case for "git blame". The list looks like:

   ...
   1091 koffice/kword/kwview.cc
   1099 kdelibs/khtml/khtml_part.cpp
   1116 koffice/kpresenter/kpresenter_view.cc
   1171 kdevelop/ChangeLog
   1667 kde-common/accounts

and while "git blame" is slow on them, it's not *painfully* so. It took 13s to get the kdevelop/ChangeLog blame, and 31s (probably because the diffs are much more interesting) to get the kpresenter_view.cc blame. Too slow, but still usable, and "git gui" again made it more interesting to wait for it..

That said, the more I look at this, the more I think that this is *the* perfect example of why you shouldn't put everything in one big repository. Git should be able to handle it, but nobody should really do things like that. It's just stupid.

I will think hard about submodules.

			Linus

On 4/5/07, Linus Torvalds <torvalds@linux-foundation.org> wrote:

Imagine how much longer it'd take if it were being served up from my home connection. :)

Many thanks to hpa for putting this up!

-clee

Thanks.  Slurping now.

On my Mac OS X system, cloning this fails with:

potomac:~/kde%git clone http://userweb.kernel.org/~hpa/kdegit/kde.git Initialized empty Git repository in /Users/bosch/kde/kde/.git/ Getting alternates list for http://userweb.kernel.org/~hpa/kdegit/ kde.git/ Getting pack list for http://userweb.kernel.org/~hpa/kdegit/kde.git/ Getting index for pack c3df59bc67f69b3861ebef8de308156f1c5fe017 Getting pack c3df59bc67f69b3861ebef8de308156f1c5fe017 which contains ca908d2d51f154aab9f5727c1e57fb23a2942485 fatal: packfile /Users/bosch/kde/kde/.git/objects/pack/pack- c3df59bc67f69b3861ebef8de308156f1c5fe017.pack cannot be mapped.

Even worse, al files seem to have been deleted, so I have to download this again. I guess, I shouldn't have used git clone...

   -Geert

On Fri, 6 Apr 2007, Geert Bosch wrote:

Given that this repo is pushing it to the limits, you better download the .tar.bz2 archive and play with it locally first.

Nicolas