Thanks for the additional information; I'll put this on my list of
things to consider for performance optimization.
-John-
On Sun, Dec 8, 2024 at 10:56 PM D. Wythe <alibuda@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> On 12/6/24 3:49 AM, John Ousterhout wrote:
> > On Sun, Dec 1, 2024 at 7:51 PM D. Wythe <alibuda@xxxxxxxxxxxxxxxxx> wrote:
> >>> +int homa_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
> >>> + unsigned int optlen)
> >>> +{
> >>> + struct homa_sock *hsk = homa_sk(sk);
> >>> + struct homa_set_buf_args args;
> >>> + int ret;
> >>> +
> >>> + if (level != IPPROTO_HOMA || optname != SO_HOMA_SET_BUF ||
> >>> + optlen != sizeof(struct homa_set_buf_args))
> >>> + return -EINVAL;
> >>
> >> SO_HOMA_SET_BUF is a bit odd here, maybe HOMA_RCVBUF ? which also can be
> >> implemented in getsockopt.
> >
> > I have changed it to HOMA_RCVBUF (and renamed struct homa_set_buf_args
> > to struct homa_rcvbuf_args). I also implemented getsockopt for
> > HOMA_RCVBUF.
> >
> >>> +
> >>> + if (copy_from_sockptr(&args, optval, optlen))
> >>> + return -EFAULT;
> >>> +
> >>> + /* Do a trivial test to make sure we can at least write the first
> >>> + * page of the region.
> >>> + */
> >>> + if (copy_to_user((__force void __user *)args.start, &args, sizeof(args)))
> >>> + return -EFAULT;
> >>
> >> To share buffer between kernel and userspace, maybe you should refer to the implementation of
> >> io_pin_pbuf_ring()
> >
> > I'm not sure what you mean here. Are you suggesting that I look at the
> > code of io_pin_pbuf_ring to make sure I've done everything needed to
> > share buffers? I don't believe that Homa needs to do anything special
> > (e.g. it doesn't need to pin the user's buffers); it just saves the
> > address and makes copy_to_user calls later when needed (and these
> > calls are all done at syscall level in the context of the
> > application). Is there something I'm missing?
> >
>
> I just thought that since the received buffer is shared between kernel and user-space, if using
> vmap() to map the very memory, so that we don't need to use such "copy_to_user" to transfer the data
> from kernel to user-space, we can use memcpy() instead. This shall be more faster, but I had no
> relevant data to prove it..
>
> So I'm not going to insist on it, it ups to you.
>
> D. Wythe
