Re: [Qemu-devel] [PATCH 10/17] migration-local: override save_page for page transmit

[Lei Li]

On 11/26/2013 07:22 PM, Paolo Bonzini wrote:
> Il 21/11/2013 10:11, Lei Li ha scritto:
> > This patch implements save_page callback for the outside
> > of page flipping. It will write the address of the page
> > on the Unix socket and flip the page data on pipe by
> > vmsplice(). Every page address would have a header flag
> > RAM_SAVE_FLAG_HOOK, which will trigger the load hook to
> > receive it in incoming side as well.
> >
> > Signed-off-by: Lei Li <address@hidden>
> > ---
> >   migration-local.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >   1 files changed, 54 insertions(+), 0 deletions(-)
> >
> > diff --git a/migration-local.c b/migration-local.c
> > index 0f0896b..14207e9 100644
> > --- a/migration-local.c
> > +++ b/migration-local.c
> > @@ -200,6 +200,59 @@ static int qemu_local_send_pipefd(QEMUFile *f, void 
> > *opaque,
> >       return 0;
> >   }
> >   
> > +static size_t qemu_local_save_ram(QEMUFile *f, void *opaque,
> > +                                  MemoryRegion *mr, ram_addr_t offset,
> > +                                  size_t size, int *bytes_sent)
> > +{
> > +    QEMUFileLocal *s = opaque;
> > +    ram_addr_t current_addr = mr->ram_addr + offset;
> > +    void *ram_addr;
> > +    ssize_t ret;
> > +
> > +    if (s->unix_page_flipping) {
> > +        qemu_fflush(s->file);
> > +        qemu_put_be64(s->file, RAM_SAVE_FLAG_HOOK);
> > +
> > +        /* Write page address to unix socket */
> > +        qemu_put_be64(s->file, current_addr);
> > +
> You can write current_addr | RAM_SAVE_FLAG_HOOK.  The value will be in
> the flags argument of the hook_ram_load, you can extract it with "flags
> & ~RAM_SAVE_FLAG_HOOK".  This cuts by half the data written to the Unix
> socket.

OK, thanks.

> Paolo
>
> > +        ram_addr = memory_region_get_ram_ptr(mr) + offset;
> > +
> > +        /* vmsplice page data to pipe */
> > +        struct iovec iov = {
> > +            .iov_base = ram_addr,
> > +            .iov_len  = size,
> > +        };
> > +
> > +        /*
> > +         * The flag SPLICE_F_MOVE is introduced in kernel for the page
> > +         * flipping feature in QEMU, which will movie pages rather than
> > +         * copying, previously unused.
> > +         *
> > +         * If a move is not possible the kernel will transparently falls
> > +         * back to copying data.
> > +         *
> > +         * For older kernels the SPLICE_F_MOVE would be ignored and a copy
> > +         * would occur.
> > +         */
> > +        ret = vmsplice(s->pipefd[1], &iov, 1, SPLICE_F_GIFT | SPLICE_F_MOVE);
> > +        if (ret == -1) {
> > +            if (errno != EAGAIN && errno != EINTR) {
> > +                fprintf(stderr, "vmsplice save error: %s\n", strerror(errno));
> > +                return ret;
> > +            }
> > +        } else {
> > +            if (bytes_sent) {
> > +                *bytes_sent = 1;
> > +            }
> > +            DPRINTF("block_offset: %lu, offset: %lu\n", block_offset, offset);
> > +            return 0;
> > +        }
> > +    }
> > +
> > +    return RAM_SAVE_CONTROL_NOT_SUPP;
> > +}
> > +
> >   static const QEMUFileOps pipe_read_ops = {
> >       .get_fd        = qemu_local_get_sockfd,
> >       .get_buffer    = qemu_local_get_buffer,
> > @@ -211,6 +264,7 @@ static const QEMUFileOps pipe_write_ops = {
> >       .writev_buffer      = qemu_local_writev_buffer,
> >       .close              = qemu_local_close,
> >       .before_ram_iterate = qemu_local_send_pipefd,
> > +    .save_page          = qemu_local_save_ram
> >   };
> >   
> >   QEMUFile *qemu_fopen_socket_local(int sockfd, const char *mode)


--
Lei