[dpdk-dev] [PATCH v2] vhost: avoid populate guest memory
Maxime Coquelin
maxime.coquelin at redhat.com
Fri Mar 30 10:21:26 CEST 2018
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 at redhat.com
>
> Signed-off-by: Jianfeng Tan <jianfeng.tan at 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 at redhat.com>
Thanks,
Maxime
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