Re: [dpdk-dev] [PATCH v3 13/15] vhost: cache address translation result

[Tiwei Bie <tiwei.bie@intel.com>]

On Thu, Sep 26, 2019 at 01:13:27AM +0800, Marvin Liu wrote:
> Cache address translation result and use it in next translation. Due
> to limited regions are supported, buffers are most likely in same
> region when doing data transmission.
> 
> Signed-off-by: Marvin Liu <yong.liu@intel.com>
> 
> diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
> index 7fb172912..d90235cd6 100644
> --- a/lib/librte_vhost/rte_vhost.h
> +++ b/lib/librte_vhost/rte_vhost.h
> @@ -91,10 +91,18 @@ struct rte_vhost_mem_region {
>  	int fd;
>  };
>  
> +struct rte_vhost_mem_region_cache {
> +	uint64_t guest_phys_addr;
> +	uint64_t guest_phys_addr_end;
> +	int64_t host_user_addr_offset;
> +	uint64_t size;
> +};
> +
>  /**
>   * Memory structure includes region and mapping information.
>   */
>  struct rte_vhost_memory {
> +	struct rte_vhost_mem_region_cache cache_region;

This breaks ABI.

>  	uint32_t nregions;
>  	struct rte_vhost_mem_region regions[];
>  };
> @@ -232,11 +240,30 @@ rte_vhost_va_from_guest_pa(struct rte_vhost_memory *mem,
>  	struct rte_vhost_mem_region *r;
>  	uint32_t i;
>  
> +	struct rte_vhost_mem_region_cache *r_cache;
> +	/* check with cached region */
> +	r_cache = &mem->cache_region;
> +	if (likely(gpa >= r_cache->guest_phys_addr && gpa <
> +		   r_cache->guest_phys_addr_end)) {
> +		if (unlikely(*len > r_cache->guest_phys_addr_end - gpa))
> +			*len = r_cache->guest_phys_addr_end - gpa;
> +
> +		return gpa - r_cache->host_user_addr_offset;
> +	}

Does this help a lot in performance?
We can implement this caching for builtin backend first.


> +
> +
>  	for (i = 0; i < mem->nregions; i++) {
>  		r = &mem->regions[i];
>  		if (gpa >= r->guest_phys_addr &&
>  		    gpa <  r->guest_phys_addr + r->size) {
>  
> +			r_cache->guest_phys_addr = r->guest_phys_addr;
> +			r_cache->guest_phys_addr_end = r->guest_phys_addr +
> +						       r->size;
> +			r_cache->size = r->size;
> +			r_cache->host_user_addr_offset = r->guest_phys_addr -
> +							 r->host_user_addr;
> +
>  			if (unlikely(*len > r->guest_phys_addr + r->size - gpa))
>  				*len = r->guest_phys_addr + r->size - gpa;
>  
> -- 
> 2.17.1
>