Take an effort to recode the arm64 vdso code from assembler to C previously submitted by Andrew Pinski <[email protected]>, rework it for use in both arm and arm64, overlapping any optimizations for each architecture. But instead of landing it in arm64, land the result into lib/vdso and unify both implementations to simplify future maintenance. This will act as the basis for implementing arm64 vdso32 in the future.
[email protected] made the following claims in the original patch: This allows the compiler to optimize the divide by 1000 and remove the other divides. On ThunderX, gettimeofday improves by 32%. On ThunderX 2, gettimeofday improves by 18%. Note I noticed a bug in the old implementation of __kernel_clock_getres; it was checking only the lower 32bits of the pointer; this would work for most cases but could fail in a few. Signed-off-by: Mark Salyzyn <[email protected]> Cc: James Morse <[email protected]> Cc: Russell King <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Will Deacon <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Dmitry Safonov <[email protected]> Cc: John Stultz <[email protected]> Cc: Mark Rutland <[email protected]> Cc: Laura Abbott <[email protected]> Cc: Kees Cook <[email protected]> Cc: Ard Biesheuvel <[email protected]> Cc: Andy Gross <[email protected]> Cc: Kevin Brodsky <[email protected]> Cc: Andrew Pinski <[email protected]> Cc: [email protected] Cc: [email protected] v2: - split first CL into 7 pieces, there were cosmetic adjustments. - make sure profiling is turned off. - kept quiet_cmd_vdsoas. v3: - changed are a result of private email review comments - rebase - move arch/arm/vdso/vgettimeofday.c to lib/vdso/vgettimeofday.c - adjust vgettimeofday.c to be a better global candidate, switch to using ARCH_PROVIDES_TIMER and __arch_counter_get() as more generic. - do not expose gettimeofday if arch does not support user space timer
