Re: [dpdk-dev] [PATCH v1 1/2] eal/x86: add WC store function

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Radu,

> 
> Add rte_write32_wc function that implements a WC store
> using movdiri instruction.

Probably worth to add 1-2 lines of text
explaining what are the advantages (perf improvement or whatever). 

> 
> Signed-off-by: Radu Nicolau <radu.nicolau@intel.com>
> ---
>  lib/librte_eal/x86/include/rte_io.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/lib/librte_eal/x86/include/rte_io.h b/lib/librte_eal/x86/include/rte_io.h
> index 2db71b1..3d74bec 100644
> --- a/lib/librte_eal/x86/include/rte_io.h
> +++ b/lib/librte_eal/x86/include/rte_io.h
> @@ -11,6 +11,26 @@ extern "C" {
> 
>  #include "generic/rte_io.h"
> 
> +/**
> + * Write a 32-bit value to I/O device memory address *addr*.
> + * Uses MOVDIRI instruction to perform a direct-store operation using WC
> + * memory write protocol.
> + *
> + * @param value
> + *  Value to write
> + * @param addr
> + *  I/O memory address to write the value to
> + */
> +static __rte_always_inline void
> +rte_write32_wc(uint32_t value, volatile void *addr)
> +{
> +	asm volatile("sfence\n\t"

Why not rte_wmb()?

> +		/* MOVDIRI */
> +		".byte 0x40, 0x0f, 0x38, 0xf9, 0x02"
> +		:
> +		: "a" (value), "d" (addr));
> +}
> +
>  #ifdef __cplusplus
>  }
>  #endif
> --
> 2.7.4