find $RPM_BUILD_ROOT/lib/modules/ -type f -name '*.ko' | xargs xz
The quick check confirms that xz runs single-threaded [even with -T0].
A shell script can implement parallelism for cases such as this.
A similar task scheme appears in dracut. At one time [~2014] these files:
90kernel-modules/module-setup.sh
40network/module-setup.sh
contained code that I wrote:
# Use two parallel streams to filter alternating modules.
local merge side2
( ( local _f1 _f2
while read _f1; do echo "$_f1"
if read _f2; then echo "$_f2" 1>&${side2}; fi
done \
| bmf1 1>&${merge} ) {side2}>&1 \
| bmf1 ) {merge}>&1
/bin/bash has some extended features which facilitate allocating
and using the file descriptors; see "REDIRECTION" in $(man bash).
For other shells: hard-wire the fd to fixed integers, document it,
and prevent collisions "manually".
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