| Message ID | 20231122133754.1240687-1-maz@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Get rid of ARM64_HAS_NO_HW_PREFETCH | expand |
On Wed, Nov 22, 2023 at 01:37:54PM +0000, Marc Zyngier wrote: > Back in 2016, it was argued that implementations lacking a HW > prefetcher could be helped by sprinkling a number of PRFM > instructions in strategic locations. > > In 2023, the one platform that presumably needed this hack is no > longer in active use (let alone maintained), and an quick > experiment shows dropping this hack only leads to a 0.4% drop > on a full kernel compilation (tested on a MT30-GS0 48 CPU system). > > Given that this is pretty much in the noise department and that > it may give odd ideas to other implementers, drop the hack for > good. > > Suggested-by: Will Deacon <will@kernel.org> > Suggested-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Marc Zyngier <maz@kernel.org> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
On Wed, 22 Nov 2023 13:37:54 +0000, Marc Zyngier wrote: > Back in 2016, it was argued that implementations lacking a HW > prefetcher could be helped by sprinkling a number of PRFM > instructions in strategic locations. > > In 2023, the one platform that presumably needed this hack is no > longer in active use (let alone maintained), and an quick > experiment shows dropping this hack only leads to a 0.4% drop > on a full kernel compilation (tested on a MT30-GS0 48 CPU system). > > [...] Applied to arm64 (for-next/cpufeature), thanks! [1/1] arm64: Get rid of ARM64_HAS_NO_HW_PREFETCH https://git.kernel.org/arm64/c/103423ad7e56 Cheers,
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 646591c67e7a..b335da126e86 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1584,16 +1584,6 @@ static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry, return has_sre; } -static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry, int __unused) -{ - u32 midr = read_cpuid_id(); - - /* Cavium ThunderX pass 1.x and 2.x */ - return midr_is_cpu_model_range(midr, MIDR_THUNDERX, - MIDR_CPU_VAR_REV(0, 0), - MIDR_CPU_VAR_REV(1, MIDR_REVISION_MASK)); -} - static bool has_cache_idc(const struct arm64_cpu_capabilities *entry, int scope) { @@ -2321,12 +2311,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { ARM64_CPUID_FIELDS(ID_AA64ISAR0_EL1, ATOMIC, IMP) }, #endif /* CONFIG_ARM64_LSE_ATOMICS */ - { - .desc = "Software prefetching using PRFM", - .capability = ARM64_HAS_NO_HW_PREFETCH, - .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, - .matches = has_no_hw_prefetch, - }, { .desc = "Virtualization Host Extensions", .capability = ARM64_HAS_VIRT_HOST_EXTN, diff --git a/arch/arm64/lib/copy_page.S b/arch/arm64/lib/copy_page.S index c336d2ffdec5..6a56d7cf309d 100644 --- a/arch/arm64/lib/copy_page.S +++ b/arch/arm64/lib/copy_page.S @@ -18,13 +18,6 @@ * x1 - src */ SYM_FUNC_START(__pi_copy_page) -alternative_if ARM64_HAS_NO_HW_PREFETCH - // Prefetch three cache lines ahead. - prfm pldl1strm, [x1, #128] - prfm pldl1strm, [x1, #256] - prfm pldl1strm, [x1, #384] -alternative_else_nop_endif - ldp x2, x3, [x1] ldp x4, x5, [x1, #16] ldp x6, x7, [x1, #32] @@ -39,10 +32,6 @@ alternative_else_nop_endif 1: tst x0, #(PAGE_SIZE - 1) -alternative_if ARM64_HAS_NO_HW_PREFETCH - prfm pldl1strm, [x1, #384] -alternative_else_nop_endif - stnp x2, x3, [x0, #-256] ldp x2, x3, [x1] stnp x4, x5, [x0, #16 - 256] diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps index b98c38288a9d..0eb2a2d2f783 100644 --- a/arch/arm64/tools/cpucaps +++ b/arch/arm64/tools/cpucaps @@ -40,7 +40,6 @@ HAS_LDAPR HAS_LSE_ATOMICS HAS_MOPS HAS_NESTED_VIRT -HAS_NO_HW_PREFETCH HAS_PAN HAS_S1PIE HAS_RAS_EXTN
Back in 2016, it was argued that implementations lacking a HW prefetcher could be helped by sprinkling a number of PRFM instructions in strategic locations. In 2023, the one platform that presumably needed this hack is no longer in active use (let alone maintained), and an quick experiment shows dropping this hack only leads to a 0.4% drop on a full kernel compilation (tested on a MT30-GS0 48 CPU system). Given that this is pretty much in the noise department and that it may give odd ideas to other implementers, drop the hack for good. Suggested-by: Will Deacon <will@kernel.org> Suggested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/kernel/cpufeature.c | 16 ---------------- arch/arm64/lib/copy_page.S | 11 ----------- arch/arm64/tools/cpucaps | 1 - 3 files changed, 28 deletions(-)