Re: [dpdk-dev] [PATCH v4 1/8] eal: introduce zmm type for AVX 512-bit

["Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>]

Hi David,

Thanks for review

On 09/07/2020 14:48, David Marchand wrote:
> On Wed, Jul 8, 2020 at 10:17 PM Vladimir Medvedkin
> <vladimir.medvedkin@intel.com> wrote:
>>
>> New data type to manipulate 512 bit AVX values.
> 
> The title mentions a "zmm" type that is not added by this patch.
> 
> Maybe instead, "eal/x86: introduce AVX 512-bit type"
> 

Agree

> 
>>
>> Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>
>> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
>> ---
>>   lib/librte_eal/x86/include/rte_vect.h | 21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
>>
>> diff --git a/lib/librte_eal/x86/include/rte_vect.h b/lib/librte_eal/x86/include/rte_vect.h
>> index df5a60762..ae59126bc 100644
>> --- a/lib/librte_eal/x86/include/rte_vect.h
>> +++ b/lib/librte_eal/x86/include/rte_vect.h
>> @@ -13,6 +13,7 @@
>>
>>   #include <stdint.h>
>>   #include <rte_config.h>
>> +#include <rte_common.h>
>>   #include "generic/rte_vect.h"
>>
>>   #if (defined(__ICC) || \
>> @@ -90,6 +91,26 @@ __extension__ ({                 \
>>   })
>>   #endif /* (defined(__ICC) && __ICC < 1210) */
>>
>> +#ifdef __AVX512F__
>> +
>> +typedef __m512i __x86_zmm_t;
> 
> We don't need this interim type, using the native __m512 is enough afaics.
> 

Agree

> Looking at the whole applied series:
> $ git grep -lw __x86_zmm_t
> lib/librte_eal/x86/include/rte_vect.h
> 
> 
>> +
>> +#define        ZMM_SIZE        (sizeof(__x86_zmm_t))
>> +#define        ZMM_MASK        (ZMM_SIZE - 1)
> 
> Macros in a public header need a RTE_ prefix + this is x86 specific,
> then RTE_X86_.
> 
> Looking at the whole applied series:
> $ git grep -lw ZMM_SIZE
> lib/librte_eal/x86/include/rte_vect.h
> $ git grep -lw ZMM_MASK
> lib/librte_eal/x86/include/rte_vect.h
> 
> So I wonder if we need to export it or we can instead just #undef
> after the struct definition.

I think it's better to undef it

> 
> 
>> +
>> +typedef union __rte_x86_zmm  {
>> +       __x86_zmm_t      z;
>> +       ymm_t    y[ZMM_SIZE / sizeof(ymm_t)];
>> +       xmm_t    x[ZMM_SIZE / sizeof(xmm_t)];
>> +       uint8_t  u8[ZMM_SIZE / sizeof(uint8_t)];
>> +       uint16_t u16[ZMM_SIZE / sizeof(uint16_t)];
>> +       uint32_t u32[ZMM_SIZE / sizeof(uint32_t)];
>> +       uint64_t u64[ZMM_SIZE / sizeof(uint64_t)];
>> +       double   pd[ZMM_SIZE / sizeof(double)];
>> +} __rte_aligned(ZMM_SIZE) __rte_x86_zmm_t;
> 
> I don't understand this forced alignment statement.
> Would not natural alignment be enough, since all fields in this union
> have the same size?
> 

Some compilers won't align this union
https://mails.dpdk.org/archives/dev/2020-March/159591.html

> 

-- 
Regards,
Vladimir