On Wed, Jan 07, 2026 at 02:12:10PM +0100, Andreas Hindborg wrote: > "Peter Zijlstra" <[email protected]> writes: > > > On Wed, Jan 07, 2026 at 01:23:38PM +0100, Andreas Hindborg wrote: > >> Hi Alice, > >> > >> Alice Ryhl <[email protected]> writes: > >> > >> > Currently the only way for Rust code to call a static inline function is > >> > to go through a helper in rust/helpers/. This introduces performance > >> > costs due to additional function calls and also clutters backtraces and > >> > flame graphs with helper symbols. > >> > > >> > To get rid of these helper symbols, provide functionality to inline > >> > helpers into Rust using llvm-link. This option complements full LTO, by > >> > being much cheaper and avoiding incompatibility with BTF. > >> > > >> > I ran a microbenchmark showing the benefit of this. All the benchmark > >> > does is call refcount_inc() in a loop. This was chosen since refcounting > >> > is quite hot in Binder. The results are that Rust spends 6.35 ns per > >> > call vs 5.73 ns per call in C. When enabling this option, the two > >> > languages become equally fast, and disassembly confirms the exact same > >> > machine code is used (in particular there is no call to > >> > rust_helper_refcount_inc). Benchmarking Binder also results in an > >> > improvement from this change. > >> > > >> > This patch is complementary to: > >> > https://lore.kernel.org/all/[email protected]/ > >> > > >> > Signed-off-by: Alice Ryhl <[email protected]> > >> > >> I get the following modpost errors when building with this applied on top > >> of v6.19-rc4: > >> > >> ERROR: modpost: "__SCK__WARN_trap" [drivers/gpu/drm/nova/nova.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [drivers/gpu/nova-core/nova_core.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [drivers/block/rnull/rnull_mod.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_minimal.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_misc_device.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_print.ko] undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_dma.ko] undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_driver_pci.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_driver_platform.ko] > >> undefined! > >> ERROR: modpost: "__SCK__WARN_trap" [samples/rust/rust_driver_faux.ko] > >> undefined! > > > > Looks like it used the wrong static_call_mod() version, was MODULE > > defined? > > CONFIG_MODULES=y, yes > > I built without the patch first, then applied the series, enabled the > option via menuconfig and ran the build. I thought maybe some dependency > check is messed up so I retried the build from a clean state. Same > result.
No, I mean -DMODULE. Note how the quiet_cmd_bindgen target has -DMODULE, but the new quiet_cmd_rust_helper target does not.
