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

[Lei Li <lilei@linux.vnet.ibm.com>]

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 <lilei@linux.vnet.ibm.com>
>> ---
>>   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