Re: [Qemu-devel] [RFC 07/12] Store the data to send also in iovec

[Orit Wasserman <owasserm@redhat.com>]

On 03/21/2013 11:56 AM, Paolo Bonzini wrote:
> Il 21/03/2013 10:09, Orit Wasserman ha scritto:
>> All data is still copied into the static buffer.
>>
>> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
>> ---
>>  savevm.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/savevm.c b/savevm.c
>> index ec64533..d5834ca 100644
>> --- a/savevm.c
>> +++ b/savevm.c
>> @@ -114,6 +114,7 @@ void qemu_announce_self(void)
>>  /* savevm/loadvm support */
>>  
>>  #define IO_BUF_SIZE 32768
>> +#define MAX_IOV_SIZE 64
> 
> You could use IOV_MAX, or min(IOV_MAX, 64).
Sure
 The 64 should be tuned on a
> good 10G network...

You need to remember that iovec of 64 is equivalent to 32 guest pages which are 
128K data. This is a large TCP packet that will be fragmented even with jumbo frames.
I can make it configurable but not sure if it will be useful.
Micheal, what do you think?

Orit
> 
> Paolo
> 
>>  struct QEMUFile {
>>      const QEMUFileOps *ops;
>> @@ -129,6 +130,9 @@ struct QEMUFile {
>>      int buf_size; /* 0 when writing */
>>      uint8_t buf[IO_BUF_SIZE];
>>  
>> +    struct iovec iov[MAX_IOV_SIZE];
>> +    unsigned int iovcnt;
>> +
>>      int last_error;
>>  };
>>  
>> @@ -546,6 +550,7 @@ static void qemu_fflush(QEMUFile *f)
>>              f->pos += f->buf_index;
>>          }
>>          f->buf_index = 0;
>> +        f->iovcnt = 0;
>>      }
>>      if (ret < 0) {
>>          qemu_file_set_error(f, ret);
>> @@ -638,12 +643,14 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size)
>>          if (l > size)
>>              l = size;
>>          memcpy(f->buf + f->buf_index, buf, l);
>> +        f->iov[f->iovcnt].iov_base = f->buf + f->buf_index;
>> +        f->iov[f->iovcnt++].iov_len = l;
>>          f->is_write = 1;
>>          f->buf_index += l;
>>          f->bytes_xfer += l;
>>          buf += l;
>>          size -= l;
>> -        if (f->buf_index >= IO_BUF_SIZE) {
>> +        if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
>>              qemu_fflush(f);
>>              if (qemu_file_get_error(f)) {
>>                  break;
>> @@ -667,8 +674,10 @@ void qemu_put_byte(QEMUFile *f, int v)
>>      f->buf[f->buf_index++] = v;
>>      f->is_write = 1;
>>      f->bytes_xfer += 1;
>> +    f->iov[f->iovcnt].iov_base = f->buf + (f->buf_index - 1);
>> +    f->iov[f->iovcnt++].iov_len = 1;
>>  
>> -    if (f->buf_index >= IO_BUF_SIZE) {
>> +    if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
>>          qemu_fflush(f);
>>      }
>>  }
>>
>