Re: [dpdk-dev] vhost-user technical isssues

["Xie, Huawei" <huawei.xie@intel.com>]

> -----Original Message-----
> From: Linhaifeng [mailto:haifeng.lin@huawei.com]
> Sent: Wednesday, November 12, 2014 11:28 PM
> To: Xie, Huawei; 'Tetsuya Mukawa'; dev@dpdk.org
> Subject: Re: [dpdk-dev] vhost-user technical isssues
> 
> 
> 
> On 2014/11/12 5:37, Xie, Huawei wrote:
> > Hi Tetsuya:
> > There are two major technical issues in my mind for vhost-user
> implementation.
> >
> > 1) memory region map
> > Vhost-user passes us file fd and offset for each memory region. Unfortunately
> the mmap offset is "very" wrong. I discovered this issue long time ago, and also
> found
> > that I couldn't mmap the huge page file even with correct offset(need double
> check).
> > Just now I find that people reported this issue on Nov 3.
> > [Qemu-devel] [PULL 27/29] vhost-user: fix mmap offset calculation
> > Anyway, I turned to the same idea used in our DPDK vhost-cuse: only use the fd
> for region(0) to map the  whole file.
> > I think we should use this way temporarily to support qemu-2.1 as it has that
> bug.
> >
> 
> the size of region 0 is not same as the file size. may be you should mmap the
> other region.
Haifeng:

Will calculate the maximum memory size, and use any file fd to mmap it.
Here we assume the fds for different regions actually point to the same file.

In theory we should use the fd for each region to map each memory region.
In fact we could map once. This will also save address space for 1GB huge page
due to mmap alignment requirement.
> 
> region 0:
>         gpa = 0x0
>         size = 655360
>         ua = 0x2aaaaac00000
>         offset = 0
> 
> region 1:// use this region to mmap.BTW how to avoid mmap twice when there
> are two devices?
>         gpa = 0xC0000
>         size = 2146697216
>         ua = 0x2aaaaacc0000
>         offset = 786432

What do you mean by two devices?
> 
> 
> 
> > 2) what message is the indicator for vhost start/release?
> > Previously  for vhost-cuse, it has SET_BACKEND message.
> > What we should do for vhost-user?
> > SET_VRING_KICK for start?
> > What about for release?
> > Unlike the kernel virtio, the DPDK virtio in guest could be restarted.
> >
> > Thoughts?
> >
> > -huawei
> >
> >
> 
> --
> Regards,
> Haifeng