Re: [PATCH v6 3/3] power: amd power monitor support

[David Marchand <david.marchand@redhat.com>]

Hello Siva,

On Mon, Oct 9, 2023 at 4:06 PM Sivaprasad Tummala
<sivaprasad.tummala@amd.com> wrote:
>
> mwaitx allows EPYC processors to enter a implementation dependent
> power/performance optimized state (C1 state) for a specific period
> or until a store to the monitored address range.
>
> Signed-off-by: Sivaprasad Tummala <sivaprasad.tummala@amd.com>
> Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---

Please put some changelog to make life easier for reviewers (and me).

I diffed with the previous version to check what had been changed and
I see this:

 static void amd_mwaitx(const uint64_t timeout)
...
-                       "c"(2), /* enable timer */
-                       "b"(timeout));
+                       "c"(0)); /* no time-out */

I will take this series as is, but please confirm why this change was needed.


>  lib/eal/x86/rte_power_intrinsics.c | 108 ++++++++++++++++++++++-------
>  1 file changed, 84 insertions(+), 24 deletions(-)
>
> diff --git a/lib/eal/x86/rte_power_intrinsics.c b/lib/eal/x86/rte_power_intrinsics.c
> index 664cde01e9..0d2953f570 100644
> --- a/lib/eal/x86/rte_power_intrinsics.c
> +++ b/lib/eal/x86/rte_power_intrinsics.c
> @@ -17,6 +17,78 @@ static struct power_wait_status {
>         volatile void *monitor_addr; /**< NULL if not currently sleeping */
>  } __rte_cache_aligned wait_status[RTE_MAX_LCORE];
>
> +/**
> + * This functions uses UMONITOR/UMWAIT instructions and will enter C0.2 state.

Fixed while applying, function*

> + * For more information about usage of these instructions, please refer to
> + * Intel(R) 64 and IA-32 Architectures Software Developer's Manual.
> + */
> +static void intel_umonitor(volatile void *addr)
> +{
> +#if defined(RTE_TOOLCHAIN_MSVC) || defined(__WAITPKG__)
> +       /* cast away "volatile" when using the intrinsic */
> +       _umonitor((void *)(uintptr_t)addr);
> +#else
> +       /*
> +        * we're using raw byte codes for compiler versions which
> +        * don't support this instruction natively.
> +        */
> +       asm volatile(".byte 0xf3, 0x0f, 0xae, 0xf7;"
> +                       :
> +                       : "D"(addr));
> +#endif
> +}
> +
> +static void intel_umwait(const uint64_t timeout)
> +{
> +       const uint32_t tsc_l = (uint32_t)timeout;
> +       const uint32_t tsc_h = (uint32_t)(timeout >> 32);
> +#if defined(RTE_TOOLCHAIN_MSVC) || defined(__WAITPKG__)
> +       _umwait(tsc_l, tsc_h);
> +#else
> +       asm volatile(".byte 0xf2, 0x0f, 0xae, 0xf7;"
> +                       : /* ignore rflags */
> +                       : "D"(0), /* enter C0.2 */
> +                         "a"(tsc_l), "d"(tsc_h));
> +#endif
> +}
> +
> +/**
> + * This functions uses MONITORX/MWAITX instructions and will enter C1 state.
> + * For more information about usage of these instructions, please refer to
> + * AMD64 Architecture Programmer’s Manual.
> + */
> +static void amd_monitorx(volatile void *addr)
> +{
> +#if defined(__MWAITX__)

This part probably breaks build with MSVC.

I could not determine whether MSVC supports this intrinsic.
I'll rely on Tyler to fix it later.


Series applied.

-- 
David Marchand