Re: RPi 4 build time

From: Mark Millard via freebsd-arm <freebsd-arm_at_freebsd.org>
Date: Sat, 22 May 2021 13:12:23 -0700
On 2021-May-22, at 09:01, tech-lists <tech-lists at zyxst.net> wrote:

> On Fri, May 21, 2021 at 03:51:35PM -0700, Mark Millard via freebsd-arm wrote:
> 
>> So, if I read this right, you are reporting 4.5 hrs
>> for a "hot ccache" result, which I had mentioned as
>> one of the things leading to large variations in
>> reported build times.
> 
> Hi,
> 
> not sure what you mean by "hot cache"

The first time ccache is used it has no prior results
to use to avoid compiles/links: an empty cache (a form
of "cold" cache). Another form of "cold" cache could
result from changing compiler options that would change
the code generated for (nearly) every file produced so
that the cache becomes ineffective.

"hot" refers to having a significant amount of
"effective/used cache content" that makes a notable
difference in the build times. I'm not that impressed
with the terminology but it is was I've seen used the
most frequently for ccache. So I used it.

> - I always use devel/ccache-static
> as have tended to build from source throughout my time of using freebsd.
> It provides tremendous speedups and generally i'll disable it only if a
> problem arises and am debugging it, or crossing a version boundary like
> from stable to current. What I'm saying is I don't know when ccache was
> last used for building anything.

I'm confused how you can know it "provides tremendous
speedups" while simultaneously not knowing "when ccache
was last used for building anything". It sounds like you
think the 4.5 hr build might have not have been from
having a notable speed up from ccache?

Remember that when comparing to my "from scratch"
build times: in my build everything was compiled
and linked, no prior build materials around to be
reused. So I'm reporting a context where I know
how to interpret the result and I'm presenting
enough history to establish a repeatable context.

> 1. rpi4 here is clocked to 2.0GHz
> 2. ccache is in use and /var/cache/ccache has *not* been previously cleared
> (i'll clear it for next test)
> 
> 3. make cleanworld cleandir clean has been run on /usr/src
> 4. sources are at 246839
> 
> 5. this rpi4 has the following properties for its disk:
> [i] root-on-zfs
> [ii] boot-to-usb3
> [iii] 4k sectorsize forced
> [iv] encrypted swapspace
> [v] entire filesystem encryption

FYI: My build-experiment boot media are never
encrypted for the file system or swap/paging
space. Another thing I'd not thought to comment
on. As I've reported, my UFS based and ZFS based
experiments get only minor variations in
build times (variations of minutes for from-
scratch builds that take hours).

> /etc/src.conf is
> https://cloud.zyxst.net/~john/FreeBSD/rpi4-main/src.conf
> 
> make -j10 cleanworld started on Sat May 22 15:41:58 BST 2021
> make -j10 cleanworld completed on Sat May 22 15:43:23 BST 2021
> 
> make -j10 cleandir started on Sat May 22 15:43:23 BST 2021
> make -j10 cleandir completed on Sat May 22 15:43:50 BST 2021
> 
> make -j10 clean started on Sat May 22 15:43:50 BST 2021
> make -j10 clean completed on Sat May 22 15:44:11 BST 2021
> 
> make -j6 buildworld started on Sat May 22 15:44:11 BST 2021
> make -j6 buildworld completed on Sat May 22 16:20:48 BST 2021

So between 36 min and 37 min to rebuild the same version
with the same build options and compiler/link command lines
(near[?] maximal effective-ccache content that leads to
near[?] maximal avoidance of rebuild activity).

Cool.

For META_MODE builds, seeing how long it takes to go through
and discover that little or nothing needs to be rebuild would
be the build times for 2nd build from doing back-to-back builds
(not even an install to the live system between). The META_MODE
use would then prevent most rebuild activity. I've not done
such a timing in a long time and it does not approximate any
normal build time for my typical rebuild patterns. So I do not
normally time that.

I'm not claiming META_MODE is similarly effective to ccache.
In fact, I know of issues where META_MODE rebuilds files that
ccache would avoid rebuilding the same file: for example,
doing an install of a build to the live system between the
rebuilds has side effects that lead META_MODE to rebuild far
more things.

> make -j6 buildkernel started on Sat May 22 16:20:48 BST 2021
> make -j6 buildkernel completed on Sat May 22 16:49:18 BST 2021

So between 28 min and 29 min to rebuild the same version with
the same build options and compiler/link command lines
(near[?] maximal effective-ccache content).

Total between 64 min and 66 min overall for buildworld buildkernel
for the near[?] maximal effective-ccache content and needing all
the files.

Good to know. Thanks.

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
Received on Sat May 22 2021 - 20:12:23 UTC

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