On Mon, Sep 14, 2026 at 11:02:22AM -0400, John Stoffel wrote: > >>>>> "Lorenzo" == Lorenzo Stoakes (ARM) <[email protected]> writes: > > > Each kernel make invocation begins with ~30 compiler and linker runs each > > of which performs duplicate probe for a number of compiler and linker > > options. > > > This is useless work - the compiler and its version is known, so use these > > to determine which options are available, once. > > > A convention already exists for this - CC_HAS_xxx, LD_HAS_xxx in Kconfig > > files (for example, CC_HAS_COUNTED_BY), so convert these probes to Kconfig > > options where appropriate. > > > This change avoids a sublte issue with ppc32 (big endian) - clang doesn't > ^^^^^^ > > subtle
Oops! I love that I ran this through AI review several times and it missed something as simple as this :) > > > accept -fno-stack-clash-protection on this sub-target, so keep this option > > in the Makefile. > > > With gcc and clang, defconfig and allmodconfig, the recorded command > > lines are unchanged, a build with nothing to do rebuilds nothing and W=1 > > continues to function correctly. > > > Doing this improves all builds, but has a particularly positive impact on > > no-op builds (builds where nothing has changed). > > > Whole build, 128-thread Threadripper 9980X, best of N runs: > > > before after delta > > ------------------------------- > > x86 defconfig, no-op make, gcc 0.78s 0.60s -0.18s (-23%) > > x86 defconfig, no-op make, clang 0.94s 0.66s -0.28s (-30%) > > x86 defconfig, touch mm/vma.c, gcc 8.6s 8.5s -0.16s (-2%) > > x86 defconfig, touch mm/vma.c, clang 8.0s 7.7s -0.24s (-3%) > > x86 defconfig, clean, clang 29.8s 29.4s -0.37s (-1%) > > x86 allmodconfig, no-op make, gcc 12.9s 12.7s -0.23s (-2%) > > x86 allmodconfig, no-op make, clang 14.2s 13.9s -0.29s (-2%) > > x86 allmodconfig, touch mm/vma.c, clang 32.2s 31.9s -0.30s (-1%) > > Are these deltas just per-patch, but cumulative with all the previous > patches applied? > Per-patch. I let the threadripper do builds for a LONG time to accumulate these... :) -- Cheers, Lorenzo
