[dpdk-dev,v2] vhost: avoid populate guest memory

  It's not necessary to populate guest memory from vhost side unless
zerocopy is enabled or users want better performance.

Update the doc for guest memory requirement clarification.

Cc: maxime.coquelin@redhat.com

Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
---
 doc/guides/prog_guide/vhost_lib.rst | 21 +++++++++++++++++++++
 doc/guides/sample_app_ug/vhost.rst  |  9 ---------
 lib/librte_vhost/vhost_user.c       |  4 +++-
 3 files changed, 24 insertions(+), 10 deletions(-)
  

On 03/28/2018 08:56 AM, Jianfeng Tan wrote:
> It's not necessary to populate guest memory from vhost side unless
> zerocopy is enabled or users want better performance.
> 
> Update the doc for guest memory requirement clarification.
> 
> Cc: maxime.coquelin@redhat.com
> 
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>   doc/guides/prog_guide/vhost_lib.rst | 21 +++++++++++++++++++++
>   doc/guides/sample_app_ug/vhost.rst  |  9 ---------
>   lib/librte_vhost/vhost_user.c       |  4 +++-
>   3 files changed, 24 insertions(+), 10 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
> index 18227b6..f474736 100644
> --- a/doc/guides/prog_guide/vhost_lib.rst
> +++ b/doc/guides/prog_guide/vhost_lib.rst
> @@ -214,6 +214,27 @@ the vhost device from the data plane.
>   
>   When the socket connection is closed, vhost will destroy the device.
>   
> +Guest memory requirement
> +------------------------
> +
> +* Memory pre-allocation
> +
> +  For non-zerocopy, guest memory pre-allocation is not a must. This can help
> +  save of memory. If users really want the guest memory to be pre-allocated
> +  (e.g., for performance reason), we can add option ``-mem-prealloc`` when
> +  starting QEMU. Or, we can lock all memory at vhost side which will force
> +  memory to be allocated when mmap at vhost side; option --mlockall in
> +  ovs-dpdk is an example in hand.
> +
> +  For zerocopy, we force the VM memory to be pre-allocated at vhost lib when
> +  mapping the guest memory; and also we need to lock the memory to prevent
> +  pages being swapped out to disk.
> +
> +* Memory sharing
> +
> +  Make sure ``share=on`` QEMU option is given. vhost-user will not work with
> +  a QEMU version without shared memory mapping.
> +

nice write-up!

>   Vhost supported vSwitch reference
>   ---------------------------------
>   
> diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
> index a4bdc6a..da161a9 100644
> --- a/doc/guides/sample_app_ug/vhost.rst
> +++ b/doc/guides/sample_app_ug/vhost.rst
> @@ -175,15 +175,6 @@ Common Issues
>     The command above indicates how many hugepages are free to support QEMU's
>     allocation request.
>   
> -* vhost-user will not work with QEMU without the ``-mem-prealloc`` option
> -
> -  The current implementation works properly only when the guest memory is
> -  pre-allocated.
> -
> -* vhost-user will not work with a QEMU version without shared memory mapping:
> -
> -  Make sure ``share=on`` QEMU option is given.
> -
>   * Failed to build DPDK in VM
>   
>     Make sure "-cpu host" QEMU option is given.
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index 90ed211..9bd0391 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -644,6 +644,7 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
>   	uint64_t mmap_offset;
>   	uint64_t alignment;
>   	uint32_t i;
> +	int populate;
>   	int fd;
>   
>   	if (dev->mem && !vhost_memory_changed(&memory, dev->mem)) {
> @@ -714,8 +715,9 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct VhostUserMsg *pmsg)
>   		}
>   		mmap_size = RTE_ALIGN_CEIL(mmap_size, alignment);
>   
> +		populate = (dev->dequeue_zero_copy) ? MAP_POPULATE : 0;
>   		mmap_addr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
> -				 MAP_SHARED | MAP_POPULATE, fd, 0);
> +				 MAP_SHARED | populate, fd, 0);
>   
>   		if (mmap_addr == MAP_FAILED) {
>   			RTE_LOG(ERR, VHOST_CONFIG,
> 

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime
  

On 03/30/2018 10:21 AM, Maxime Coquelin wrote:
> 
> 
> On 03/28/2018 08:56 AM, Jianfeng Tan wrote:
>> It's not necessary to populate guest memory from vhost side unless
>> zerocopy is enabled or users want better performance.
>>
>> Update the doc for guest memory requirement clarification.
>>
>> Cc: maxime.coquelin@redhat.com
>>
>> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
>> ---
>>   doc/guides/prog_guide/vhost_lib.rst | 21 +++++++++++++++++++++
>>   doc/guides/sample_app_ug/vhost.rst  |  9 ---------
>>   lib/librte_vhost/vhost_user.c       |  4 +++-
>>   3 files changed, 24 insertions(+), 10 deletions(-)
>>
>> diff --git a/doc/guides/prog_guide/vhost_lib.rst 


Applied to dpdk-next-virtio/master

Thanks,
Maxime