Re: configure optimization feature update

Richard Purdie

Hi Dongxiao,

On Thu, 2011-06-16 at 08:57 +0800, Xu, Dongxiao wrote:
Recently I was doing the "configure optimization" feature and
collecting data for it.

The main logic of this feature is straight forward:

1. Use the diff file as autoreconf cache. (I use command: "diff -ruN
SOURCE-ORIG SOURCE", here "SOURCE-ORIG" is the source directory before
running autoreconf, while "SOURCE" is the directory after running
2. Add SRC_URI checksum for all patches of the source code.
3. Tag each autoreconf cache file with ${PN} and the SRC_URI checksum
of source code and all patches.
4. If the currently SRC_URI checksum matches the cached checksum, then
we can patch the cache instead of running "autoreconf" stage.

I did some testings for sato build, the result is not as good as we

On a server build machine (Genuine Intel(R) CPU @ 2.40GHz, 2 sockets with 6 core each and hyperthreading, thus 24 logical CPUs in all, 66G memory):

w/o the optimization:
real 83m40.963s
user 496m58.550s
sys 329m1.590s

w/ the optimization:
real 79m1.062s
user 460m58.600s
sys 347m42.120s

It has about 5% performance gain.
Whats interesting there is the relatively large sys times compared to
user. Any idea why that's happening? Spinning locks?

I also tested the patch on a desktop core-i7 machine (Intel(R) Core(TM) i7 CPU 870 @ 2.93GHz, 4 core 8 logical CPU, 4G memory):

w/o the optimization:
real 105m25.436s
user 372m48.040s
sys 51m23.950s

w/ the optimization:
real 103m38.314s
user 332m35.770s
sys 49m4.520s

It only has about 2% performance gain.

The result is not encouraging.
Agreed, this isn't as good as we'd hoped for :(.

There are also some other things we need to take into consideration
for this feature:

1. If add this feature, the first build time should be longer than
current since it needs to build the autoreconf cache.
2. Maintainers needs to maintain the SRC_URI checksums not only for
source code, but also all its patches. For some recipes, it has more
than 20 patches, which needs assignable maintenance effort.
3. How to distribute the caches will be a problem. The total size of
such cache is about 900M (before compression) and 200M (after
compression). Since the size is not small, distributing it with Poky
source code doesn't make sense. On another aspect, we can use
something like "sstate". But since we already have caches of sstate, I
think it is not necessary for us to enable another similar cache
mechanism with little improvement.

Therefore my opinion is we may give up this feature. What's your
comments and suggestions?
I think we should put the patches together on a branch in contrib so we
keep them somewhere in case we want them. Certainly tracking what
changes the autoreconf process makes may be useful in other situations
in future so its worth keeping the patches. I think you're right and we
should shelve the idea for now though as it doesn't look to be worth the
pain it entails.

For reference, we probably do need to start tracking the file checksums
for the benefit of sstate.

The mediocre performance improvement is likely down to the size of the
cache data but I can't immediately think of a way to improve that :(.



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