Re: [PATCH v6 7/7] vhost: optimize memcpy routines when cc memcpy is used

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2024-10-09 23:25, Morten Brørup wrote:
>> +#if defined(RTE_USE_CC_MEMCPY) && defined(RTE_ARCH_X86_64)
>> +static __rte_always_inline void
>> +pktcpy(void *restrict in_dst, const void *restrict in_src, size_t len)
>> +{
> 
> A comment describing why batch_copy_elem.dst and src point to 16 byte aligned data would be nice.
> 

Good point. As I think I mentioned at some point, I'm not sure they are.

 From what I recall, having (or pretending) the data is 16-bit aligned 
does give a noticeable performance increase on x86_64.

Is this something I should look into for 24.11, or this patch set is not 
going to make it anyway?

>> +	void *dst = __builtin_assume_aligned(in_dst, 16);
>> +	const void *src = __builtin_assume_aligned(in_src, 16);
>> +
>> +	if (len <= 256) {
>> +		size_t left;
>> +
>> +		for (left = len; left >= 32; left -= 32) {
>> +			memcpy(dst, src, 32);
>> +			dst = RTE_PTR_ADD(dst, 32);
>> +			src = RTE_PTR_ADD(src, 32);
>> +		}
>> +
>> +		memcpy(dst, src, left);
>> +	} else
>> +		memcpy(dst, src, len);
>> +}
>> +#else
>> +static __rte_always_inline void
>> +pktcpy(void *dst, const void *src, size_t len)
>> +{
>> +	rte_memcpy(dst, src, len);
>> +}
>> +#endif
>> +
>>   static inline void
>>   do_data_copy_enqueue(struct virtio_net *dev, struct vhost_virtqueue
>> *vq)
>>   	__rte_shared_locks_required(&vq->iotlb_lock)
>> @@ -240,7 +273,7 @@ do_data_copy_enqueue(struct virtio_net *dev, struct
>> vhost_virtqueue *vq)
>>   	int i;
>>
>>   	for (i = 0; i < count; i++) {
>> -		rte_memcpy(elem[i].dst, elem[i].src, elem[i].len);
>> +		pktcpy(elem[i].dst, elem[i].src, elem[i].len);
>>   		vhost_log_cache_write_iova(dev, vq, elem[i].log_addr,
>>   					   elem[i].len);
>>   		PRINT_PACKET(dev, (uintptr_t)elem[i].dst, elem[i].len, 0);
>> @@ -257,7 +290,7 @@ do_data_copy_dequeue(struct vhost_virtqueue *vq)
>>   	int i;
>>
>>   	for (i = 0; i < count; i++)
>> -		rte_memcpy(elem[i].dst, elem[i].src, elem[i].len);
>> +		pktcpy(elem[i].dst, elem[i].src, elem[i].len);
>>
>>   	vq->batch_copy_nb_elems = 0;
>>   }
>> --
>> 2.43.0
> 
> Anyway,
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
>