Re: FYI: Why META_MODE rebuilds so much for building again after installworld (no source changes)

[Added a question about a possible typo in the old original message.]

On Feb 21, 2023, at 13:31, Mark Millard <marklmi@yahoo.com> wrote:

> [This will be a question relative to the old material below.]
> 
> On Jan 27, 2021, at 17:33, Simon J. Gerraty <sjg@juniper.net> wrote:
> 
>> Mark Millard via freebsd-current <freebsd-current@FreeBSD.org> wrote:
>>>>> Given an already built, installed and booted system version, I've
>>>>> noted a big difference for META_MODE in 2 rebuild contexts (no
>>>>> source updates involved):
>>>>> 
>>>>> *) Prior buildworld buildkernel, installkernel, installworld, boot
>>>>> presumed before (A) and before (B) below.
>> 
>> Yes installworld is going to cause problems unless you tell meta mode to
>> ignore everything outside of the src/obj tree.
>> But even that isn't enough as you note below.
>> 
>>>>> So I used make -dM for the commented buildworld buildkernel lines, logging
>>>>> the build output and later diff'ing them.
>>>>> 
>>>>> Result that I noticed? Lots of lines uniquely from (B)'s case, ending with
>>>>> one of:
>>>>> 
>>>>> file '/usr/obj/amd64_clang/amd64.amd64/usr/fbsd/mm-src/amd64.amd64/tmp/legacy/usr/sbin/awk' is newer than the target...
>> 
>> Yes.  That would be expected.
>> I think Bryan added some knobs to mitigate some of this.
>> 
>> grep -n META.*IGNORE share/mk/*mk
>> 
>> might be instructive.
>> 
>>>>> Many/most/all(?) of these seem to me to be unlikely to actually need to
>>>>> contribute to what needs to be rebuilt (just based on being newer). So
>>>>> the option to ignore (some of?) them could be useful in making META_MODE
>>>>> builds quicker.
>> 
>> Yes on all counts.  That's why bmake provides a number of knobs to
>> ignore such things.
>> They are listed in the man page in increasing order of expense.
>> 
>> One of the risks of the sort of introspection meta mode does, is delving
>> too deep (like the dwarfs ;-)
>> 
>> The .MAKE.META.IGNORE_* and .MAKE.META.BAILIWICK variables help to
>> contain the potential insanity.
>> 
>>>> The following from one of the .meta files makes the point that rm use
>>>> in the example is unlikely to be important to needing to rebuild,
>>>> despite it actually causing a file rebuild. Nor is the specific echo
>>>> command listed relevant. Only the "ar" command is:
>>>> 
>>>> # Meta data file /usr/obj/amd64_clang/amd64.amd64/usr/fbsd/mm-src/amd64.amd64/lib/libc++/libc++.a.meta
>>>> CMD @echo building static c++ library
>>>> CMD @rm -f libc++.a
>>>> CMD ar -crsD libc++.a algorithm.o any.o atomic.o barrier.o bind.o
>> 
>>>> -- filemon acquired metadata --
>>>> # filemon version 5
>>>> # Target pid 22471
>>>> # Start 1611359217.214996
>>>> V 5
>>>> E 22961 /bin/sh
>>>> R 22961 /etc/libmap.conf
>>>> R 22961 /var/run/ld-elf.so.hints
>>>> R 22961 /lib/libedit.so.7
>>>> R 22961 /lib/libc.so.7
>>>> R 22961 /lib/libncursesw.so.9
>>>> R 22961 /usr/share/locale/C.UTF-8/LC_CTYPE
>>>> F 22961 22962
>>>> E 22962 /usr/obj/amd64_clang/amd64.amd64/usr/fbsd/mm-src/amd64.amd64/tmp/legacy/usr/sbin/rm
>> 
>>>> The timestamp on . . ./tmp/legacy/usr/sbin/rm is not
>>>> actually relevant to if libc++.a needs to be rebuilt.
>> 
>> True. 
>> If there is nothing under .../tmp/legacy that should be counted you can
>> just:
>> 
>> .MAKE.META_IGNORE_PATHS += that path

Was that supposed to be ("." vs. "_"):

.MAKE.META.IGNORE_PATHS += that path

The later ones listed have ".".

>> which would be the cheapest option.
>> 
>> If however there are things that should be considered you'd have to
>> use a much more specific list of .MAKE.META_IGNORE_PATHS or

(Same question applies to the above.)

>> perhaps something like:
>> 
>> .MAKE.META.IGNORE_PATTERNS += */rm
>> 
>> would ignore an rm binary regardless of where found.
>> 
>> worst case you might need something like:
>> 
>> # realpath
>> .MAKE.META.IGNORE_FILTER += tA
>> # ignore anything here
>> .MAKE.META.IGNORE_FILTER += N*/tmp/legacy/usr/bin/*
>> 
>> Unlike .MAKE.META.IGNORE_PATTERNS which is a list of patterns to match
>> the goal with .MAKE.META.IGNORE_FILTER  is to reduced to an empty string
>> paths to be ignored.
>> 
>>>> Of course, the structure also point out the judgment
>>>> is specific to understanding the sequence of CMD's
>>>> listed above. Only a hack of ignoring, not recording,
>>>> or commenting out the filemon lines ending in
>>>> /tmp/legacy/usr/sbin/rm would seem to avoid the @rm
>>>> handling issue. Such might well have its own risks.
>> 
>> No hacking needed, there are a range of knobs to help.
>> 
>>> Just for reference for more about the sequencing involved:
>>> 
>>> Looks like in my example various . . ./tmp/legacy/. . ./*bin/
>>> actually are links to files in:
>>> 
>>> /usr/obj/amd64_clang/amd64.amd64/usr/fbsd/mm-src/amd64.amd64/tmp/legacy/bin/
>>> 
>>> and the later after-install buildworld "Rebuilding the
>>> temporary build tree" step leads to the updated dates for
>>> files in that area, updated via the code that reports:
>>> 
>>> Linking host tools into /usr/obj/amd64_clang/amd64.amd64/usr/fbsd/mm-src/amd64.amd64/tmp/legacy/bin
>>> 
>>> So the prior installworld leaves updated dates and the
>>> linking to those installed files makes
>>> . . ./tmp/legacy/. . ./*bin/* have the newer dates show
>>> up for the legacy paths as well.
>>> 
>>> In turn the dependency tracking via META_MODE uses the new
>>> dates on . . ./tmp/legacy/. . ./*bin/* files to cause
>>> rebuilds of more materials than if installworld had not
>>> been done.
>>> 
>>> It is not obvious if Bryan D. would find the effort to avoid
>>> this worthwhile for the contexts that drive FreeBSD's build
>>> environment choices.
>> 
>> For people that  use installworld and also want META_MODE
>> it would seem some additional IGNORE work may be beneficial.
> 
> Since some of the paths reported ended up being links
> (symbolic, as I remember), what are the principles for
> which form of paths should be the basis for paths in
> the likes of:
> 
> .MAKE.META_IGNORE_PATHS

(The above may be a typo relative to .MAKE.META.IGNORE_PATHS .)

> .MAKE.META.IGNORE_PATTERNS
> .MAKE.META.IGNORE_FILTER
> 
> Target of link? Path to the link itself, not the
> target? Both?
> 
> (Something had interrupted my explorations back then and
> I'd forgotten about your note and have never done the
> exploration. Trying to partially answer a question on the
> lists lead to me reviewing the old thread and running into
> your note again.)
> 


===
Mark Millard
marklmi at yahoo.com