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kbuild,bpf: Pass make jobs' value to pahole

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Pass the value of make's -j/--jobs argument to pahole, to avoid out of
memory errors and make pahole respect the "jobs" value of make.

On systems with little memory but many cores, invoking pahole using -j
without argument potentially creates too many pahole instances,
causing an out-of-memory situation. Instead, we should pass make's
"jobs" value as an argument to pahole's -j, which is likely configured
to be (much) lower than the actual core count on such systems.

If make was invoked without -j, either via cmdline or MAKEFLAGS, then
JOBS will be simply empty, resulting in the existing behavior, as
expected.

Signed-off-by: Florian Schmaus <flo@geekplace.eu>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Link: https://lore.kernel.org/bpf/20241102100452.793970-1-flo@geekplace.eu
This commit is contained in:
Florian Schmaus 2024-11-02 11:04:51 +01:00 committed by Andrii Nakryiko
parent 7b6e5bfa25
commit 09048d22b7
1 changed files with 4 additions and 2 deletions
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6
scripts/Makefile.btf
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@ -3,6 +3,8 @@
pahole-ver := $(CONFIG_PAHOLE_VERSION)
pahole-flags-y :=
JOBS := $(patsubst -j%,%,$(filter -j%,$(MAKEFLAGS)))
ifeq ($(call test-le, $(pahole-ver), 125),y)
# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
@ -12,14 +14,14 @@ endif
pahole-flags-$(call test-ge, $(pahole-ver), 121) += --btf_gen_floats
pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j
pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j$(JOBS)
pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
else
# Switch to using --btf_features for v1.26 and later.
pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j$(JOBS) --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
ifneq ($(KBUILD_EXTMOD),)
module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base