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Re: bmake inefficiencies

On 26.01.2021 15:41, Mateusz Guzik wrote:
I had a look with truss at what bmake is doing and I think a lot of
the syscalls can be easily avoided. Examples come from FreeBSD with
bmake-20210110 and I don't know to what extent they are representative
for other systems.

1. spurious waitpid

when doing buildkernel I counted the following:
7010 cases of error code 0 (== nothing to do)
371 cases of ECHILD
1526 cases of reaping

I'm not familiar enough with waitpid, so I will not touch this topic.


for example mkstemp is used and FD_CLOEXEC performed on the result.
Instead mkostemp can be used and mkTempFile can accept O_CLOEXEC as an
argument to save explicit fcntl.

On current NetBSD and FreeBSD, this may be fine, for other platforms
there would need to be autoconf support.  Simon?

3. avoidable temp files

JobOpenTmpFile opens a file and later checks if anything was written
to it. Not an actual patch, but a hack to demonstrate the fix can be
found at the end. Looks like checking can be done upfront in O(1) time
(not done in the patch below).

With this in place I get the following result for buildworld:
87930 JobOpenTmpFile: created!
70564 JobOpenTmpFile: skipped!

i.e. about 44% of all temp files can be avoided at least in this workload.

This is something I understood and will tackle.  Thank you for doing the
analysis.  I think the main cause for this are chains of targets such as:

all: build
build: do-build
do-build: do-build-c
do-build-c: ${SRCS:M*.c:.c=.o}

Thanks for the patch, that looks both simple and correct.


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