| Message ID | 20201105045140.2589346-4-andrii@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | Integrate kernel module BTF support | expand |
On Wed, Nov 04, 2020 at 08:51:38PM -0800, Andrii Nakryiko wrote: > > +config DEBUG_INFO_BTF_MODULES > + bool "Generate BTF for kernel modules" > + def_bool y > + depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF Does it need to be a new config ? Can the build ran pahole if DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF ?
On Thu, Nov 5, 2020 at 7:13 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: > > On Wed, Nov 04, 2020 at 08:51:38PM -0800, Andrii Nakryiko wrote: > > > > +config DEBUG_INFO_BTF_MODULES > > + bool "Generate BTF for kernel modules" > > + def_bool y > > + depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF > > Does it need to be a new config ? > Can the build ran pahole if DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF ? It probably doesn't. If I drop the "bool" line, it will become non-configurable calculated Kconfig value, convenient to use everywhere. All the rest will stay exactly the same. It's nice to not have to do "if defined(DEBUG_INFO_BTF) && defined(MODULES) && defined(PAHOLE_HAS_SPLIT_BTF)" checks, but rather a simple "ifdef CONFIG_DEBUG_INFO_BTF_MODULES". Does that work?
On Thu, Nov 5, 2020 at 7:48 PM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Thu, Nov 5, 2020 at 7:13 PM Alexei Starovoitov > <alexei.starovoitov@gmail.com> wrote: > > > > On Wed, Nov 04, 2020 at 08:51:38PM -0800, Andrii Nakryiko wrote: > > > > > > +config DEBUG_INFO_BTF_MODULES > > > + bool "Generate BTF for kernel modules" > > > + def_bool y > > > + depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF > > > > Does it need to be a new config ? > > Can the build ran pahole if DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF ? > > It probably doesn't. If I drop the "bool" line, it will become > non-configurable calculated Kconfig value, convenient to use > everywhere. All the rest will stay exactly the same. It's nice to not > have to do "if defined(DEBUG_INFO_BTF) && defined(MODULES) && > defined(PAHOLE_HAS_SPLIT_BTF)" checks, but rather a simple "ifdef > CONFIG_DEBUG_INFO_BTF_MODULES". Does that work? Makes sense.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index d7a7bc3b6098..d3303ed58ff0 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -265,6 +265,9 @@ config DEBUG_INFO_DWARF4 But it significantly improves the success of resolving variables in gdb on optimized code. +config PAHOLE_HAS_SPLIT_BTF + def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119") + config DEBUG_INFO_BTF bool "Generate BTF typeinfo" depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED @@ -274,6 +277,13 @@ config DEBUG_INFO_BTF Turning this on expects presence of pahole tool, which will convert DWARF type info into equivalent deduplicated BTF type info. +config DEBUG_INFO_BTF_MODULES + bool "Generate BTF for kernel modules" + def_bool y + depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF + help + Generate compact split BTF type information for kernel modules. + config GDB_SCRIPTS bool "Provide GDB scripts for kernel debugging" help diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal index ae01baf96f4e..02b892421f7a 100644 --- a/scripts/Makefile.modfinal +++ b/scripts/Makefile.modfinal @@ -6,6 +6,7 @@ PHONY := __modfinal __modfinal: +include include/config/auto.conf include $(srctree)/scripts/Kbuild.include # for c_flags @@ -36,8 +37,23 @@ quiet_cmd_ld_ko_o = LD [M] $@ -T scripts/module.lds -o $@ $(filter %.o, $^); \ $(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true) -$(modules): %.ko: %.o %.mod.o scripts/module.lds FORCE - +$(call if_changed,ld_ko_o) +quiet_cmd_btf_ko = BTF [M] $@ + cmd_btf_ko = LLVM_OBJCOPY=$(OBJCOPY) $(PAHOLE) -J --btf_base vmlinux $@ + +# Same as newer-prereqs, but allows to exclude specified extra dependencies +newer_prereqs_except = $(filter-out $(PHONY) $(1),$?) + +# Same as if_changed, but allows to exclude specified extra dependencies +if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \ + $(cmd); \ + printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:) + +# Re-generate module BTFs if either module's .ko or vmlinux changed +$(modules): %.ko: %.o %.mod.o scripts/module.lds vmlinux FORCE + +$(call if_changed_except,ld_ko_o,vmlinux) +ifdef CONFIG_DEBUG_INFO_BTF_MODULES + +$(if $(newer-prereqs),$(call cmd,btf_ko)) +endif targets += $(modules) $(modules:.ko=.mod.o)
Add Kconfig option to generate kernel module split BTFs, if pahole's version support it. Kernel module BTF has to be re-grenerated if either vmlinux's BTF changes or .ko changes. To achieve that, I needed a helper similar to if_changed, but that would allow to filter out vmlinux from the list of updated dependencies for .ko building. I've put it next to the only place that uses and needs it, but it might be a better idea to just add it along the other if_changed variants into scripts/Kbuild.include. Each kernel module's BTF deduplication is pretty fast, as it does only incremental BTF deduplication on top of already deduplicated vmlinux BTF. To show the added build time, I've first ran make only just built kernel (to establish the baseline) and then forced only BTF re-generation, without regenerating .ko files. The build was performed with -j60 parallelization on 56-core machine. The final time also includes bzImage building, so it's not a pure BTF overhead. $ time make -j60 ... make -j60 27.65s user 10.96s system 782% cpu 4.933 total $ touch ~/linux-build/default/vmlinux && time make -j60 ... make -j60 123.69s user 27.85s system 1566% cpu 9.675 total So 4.6 seconds real time, with noticeable part spent in compressed vmlinux and bzImage building. To show size savings, I've built my kernel configuration with about 700 kernel modules with full BTF per each kernel module (without deduplicating against vmlinux) and with split BTF against deduplicated vmlinux (approach in this patch). Below are top 10 modules with biggest BTF sizes. And total size of BTF data across all kernel modules. It shows that split BTF "compresses" 115MB down to 5MB total. And the biggest kernel modules get a downsize from 500-570KB down to 200-300KB. FULL BTF ======== $ for f in $(find . -name '*.ko'); do size -A -d $f | grep BTF | awk '{print $2}'; done | awk '{ s += $1 } END { print s }' 115710691 $ for f in $(find . -name '*.ko'); do printf "%s %d\n" $f $(size -A -d $f | grep BTF | awk '{print $2}'); done | sort -nr -k2 | head -n10 ./drivers/gpu/drm/i915/i915.ko 570570 ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko 520240 ./drivers/gpu/drm/radeon/radeon.ko 503849 ./drivers/infiniband/hw/mlx5/mlx5_ib.ko 491777 ./fs/xfs/xfs.ko 411544 ./drivers/net/ethernet/intel/i40e/i40e.ko 403904 ./drivers/net/ethernet/broadcom/bnx2x/bnx2x.ko 398754 ./drivers/infiniband/core/ib_core.ko 397224 ./fs/cifs/cifs.ko 386249 ./fs/nfsd/nfsd.ko 379738 SPLIT BTF ========= $ for f in $(find . -name '*.ko'); do size -A -d $f | grep BTF | awk '{print $2}'; done | awk '{ s += $1 } END { print s }' 5194047 $ for f in $(find . -name '*.ko'); do printf "%s %d\n" $f $(size -A -d $f | grep BTF | awk '{print $2}'); done | sort -nr -k2 | head -n10 ./drivers/gpu/drm/i915/i915.ko 293206 ./drivers/gpu/drm/radeon/radeon.ko 282103 ./fs/xfs/xfs.ko 222150 ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko 198503 ./drivers/infiniband/hw/mlx5/mlx5_ib.ko 198356 ./drivers/net/ethernet/broadcom/bnx2x/bnx2x.ko 113444 ./fs/cifs/cifs.ko 109379 ./arch/x86/kvm/kvm.ko 100225 ./drivers/gpu/drm/drm.ko 94827 ./drivers/infiniband/core/ib_core.ko 91188 Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- lib/Kconfig.debug | 10 ++++++++++ scripts/Makefile.modfinal | 20 ++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-)