On 2014/11/14 9:28, Xie, Huawei wrote: > > >> -----Original Message----- >> From: Linhaifeng [mailto:haifeng.lin at huawei.com] >> Sent: Wednesday, November 12, 2014 11:28 PM >> To: Xie, Huawei; 'Tetsuya Mukawa'; dev at 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.
actually there may be two hugepage files created by qemu. one day i create a 4G VM found qemu create 2 hugepage file and send them to vhost-user. you can try to test it. > > 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? >> >> e.g there are two vhost-user backends in a VM, we will receive two SET_MEM_TABLE messages, actually we only need mmap once in one message. I think qemu should add a new message to send all hugepage fd and size once. as this we not need to mmap and calculate memory in set_mem_table message. >> >>> 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 > > > . > -- Regards, Haifeng
