Re: [PATCH 2/2] x86/fpu: Support disabling AVX and AVX512
From: Andi Kleen
Date: Wed Apr 19 2017 - 19:03:27 EST
Ping! Any comments on these patches? If ok please consider merging.
Thanks,
-Andi
On Sat, Mar 11, 2017 at 09:30:57AM -0800, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> For performance testing it is useful to be able to disable AVX
> and AVX512. User programs check in XGETBV if AVX is supported
> by the OS. If we don't initialize the XSAVE state for AVX it will
> appear as if the OS is not supporting AVX.
>
> Implement disable options for AVX and AVX512 code in the XSAVE code.
>
> v2: Change description. Make variable static. Remove Intel reference.
> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 3 ++
> arch/x86/kernel/fpu/xstate.c | 61 +++++++++++++++++++++----
> 2 files changed, 55 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 2ba45caabada..b94ff507a48f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -785,6 +785,9 @@
> dhash_entries= [KNL]
> Set number of hash buckets for dentry cache.
>
> + disable_avx [X86] Disable support for AVX
> + disable_avx512 [X86] Disable support for AVX512
> +
> disable_1tb_segments [PPC]
> Disables the use of 1TB hash page table segments. This
> causes the kernel to fall back to 256MB segments which
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index c24ac1efb12d..977ab03eacf7 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -16,6 +16,20 @@
>
> #include <asm/tlbflush.h>
>
> +enum xsave_features {
> + XSAVE_X87,
> + XSAVE_SSE,
> + XSAVE_AVX,
> + XSAVE_MPX_BOUNDS,
> + XSAVE_MPX_CSR,
> + XSAVE_AVX512_OPMASK,
> + XSAVE_AVX512_HI256,
> + XSAVE_AVX512_ZMM_HI256,
> + XSAVE_PT,
> + XSAVE_PKU,
> + XSAVE_UNKNOWN
> +};
> +
> /*
> * Although we spell it out in here, the Processor Trace
> * xfeature is completely unused. We use other mechanisms
> @@ -41,6 +55,8 @@ static const char *xfeature_names[] =
> */
> u64 xfeatures_mask __read_mostly;
>
> +static u64 xfeatures_disabled __initdata;
> +
> static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
> static unsigned int xstate_sizes[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
> static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];
> @@ -52,6 +68,21 @@ static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];
> */
> unsigned int fpu_user_xstate_size;
>
> +static void clear_avx512(void)
> +{
> + setup_clear_cpu_cap(X86_FEATURE_AVX512F);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512IFMA);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512PF);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512ER);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512CD);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512DQ);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512BW);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512VL);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512VBMI);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512_4VNNIW);
> + setup_clear_cpu_cap(X86_FEATURE_AVX512_4FMAPS);
> +}
> +
> /*
> * Clear all of the X86_FEATURE_* bits that are unavailable
> * when the CPU has no XSAVE support.
> @@ -64,17 +95,9 @@ void fpu__xstate_clear_all_cpu_caps(void)
> setup_clear_cpu_cap(X86_FEATURE_XSAVES);
> setup_clear_cpu_cap(X86_FEATURE_AVX);
> setup_clear_cpu_cap(X86_FEATURE_AVX2);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512F);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512IFMA);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512PF);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512ER);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512CD);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512DQ);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512BW);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512VL);
> + clear_avx512();
> setup_clear_cpu_cap(X86_FEATURE_MPX);
> setup_clear_cpu_cap(X86_FEATURE_XGETBV1);
> - setup_clear_cpu_cap(X86_FEATURE_AVX512VBMI);
> setup_clear_cpu_cap(X86_FEATURE_PKU);
> setup_clear_cpu_cap(X86_FEATURE_AVX512_4VNNIW);
> setup_clear_cpu_cap(X86_FEATURE_AVX512_4FMAPS);
> @@ -735,6 +758,7 @@ void __init fpu__init_system_xstate(void)
> goto out_disable;
> }
>
> + xfeatures_mask &= ~xfeatures_disabled;
> xfeatures_mask &= fpu__get_supported_xfeatures_mask();
>
> /* Enable xstate instructions to be able to continue with initialization: */
> @@ -1080,3 +1104,22 @@ int copyin_to_xsaves(const void *kbuf, const void __user *ubuf,
>
> return 0;
> }
> +
> +static int __init parse_disable_avx512(char *str)
> +{
> + xfeatures_disabled |= BIT(XSAVE_AVX512_OPMASK) |
> + BIT(XSAVE_AVX512_HI256) |
> + BIT(XSAVE_AVX512_ZMM_HI256);
> + clear_avx512();
> + return 0;
> +}
> +early_param("disable_avx512", parse_disable_avx512);
> +
> +static int __init parse_disable_avx(char *str)
> +{
> + xfeatures_disabled |= BIT(XSAVE_AVX);
> + setup_clear_cpu_cap(X86_FEATURE_AVX);
> + setup_clear_cpu_cap(X86_FEATURE_AVX2);
> + return parse_disable_avx512(NULL);
> +}
> +early_param("disable_avx", parse_disable_avx);
> --
> 2.9.3
>