On 6/30/22 05:42, Chang S. Bae wrote:
> Explain steps to enable the dynamic feature with a code example.
>
> Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
> Reviewed-by: Thiago Macieira <thiago.macieira@xxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> Changes from v1:
> * Update the description without mentioning CPUID & XGETBV (Dave Hansen).
> ---
> Documentation/x86/xstate.rst | 42 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 42 insertions(+)
>
> diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst
> index 5cec7fb558d6..c439901419fb 100644
> --- a/Documentation/x86/xstate.rst
> +++ b/Documentation/x86/xstate.rst
> @@ -64,6 +64,48 @@ the handler allocates a larger xstate buffer for the task so the large
> state can be context switched. In the unlikely cases that the allocation
> fails, the kernel sends SIGSEGV.
>
> +AMX TILE_DATA enabling example
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +The following steps dynamically enable TILE_DATA:
> +
This should be "Below is the example of how userspace applications enable
TILE_DATA dynamically:"
> + 1. An application first needs to determine the feature support::
> +
Better say "The application first needs to query the kernel for AMX
support".
> + #include <asm/prctl.h>
> + #include <sys/syscall.h>
> + #include <stdio.h>
> + #include <unistd.h>
> +
> + #define ARCH_GET_XCOMP_SUPP 0x1021
> +
> + #define XFEATURE_XTILECFG 17
> + #define XFEATURE_XTILEDATA 18
> + #define XFEATURE_MASK_XTILE ((1 << XFEATURE_XTILECFG) | (1 << XFEATURE_XTILEDATA))
> +
> + unsigned long features;
> + long rc;
> +
> + ...
> +
> + rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_SUPP, &features);
> +
> + if (!rc && (features & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE)
> + printf("AMX is available.\n");
> +
> + 2. After determining support for AMX, an application must explicitly ask
> + permission to use it::
> +
Shorter is "After that,..."
> + #define ARCH_REQ_XCOMP_PERM 0x1023
> +
> + ...
> +
> + rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA);
> +
> + if (!rc)
> + printf("AMX is ready for use.\n");
> +
> +Note this example does not include the sigaltstack preparation.
> +
I guess "application" here means userspace application, right?
--
An old man doll... just what I always wanted! - Clara
