Take an effort to recode the arm64 vdso code from assembler to C previously submitted by Andrew Pinski <apin...@cavium.com>, 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.
apin...@cavium.com 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 <saly...@android.com> Cc: James Morse <james.mo...@arm.com> Cc: Russell King <li...@armlinux.org.uk> Cc: Catalin Marinas <catalin.mari...@arm.com> Cc: Will Deacon <will.dea...@arm.com> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Dmitry Safonov <dsafo...@virtuozzo.com> Cc: John Stultz <john.stu...@linaro.org> Cc: Mark Rutland <mark.rutl...@arm.com> Cc: Laura Abbott <labb...@redhat.com> Cc: Kees Cook <keesc...@chromium.org> Cc: Ard Biesheuvel <ard.biesheu...@linaro.org> Cc: Andy Gross <andy.gr...@linaro.org> Cc: Kevin Brodsky <kevin.brod...@arm.com> Cc: Andrew Pinski <apin...@cavium.com> Cc: linux-kernel@vger.kernel.org Cc: linux-arm-ker...@lists.infradead.org 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
