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

[Orit Wasserman <owasserm@redhat.com>]

On 03/21/2013 01:14 PM, Michael S. Tsirkin wrote:
> On Thu, Mar 21, 2013 at 01:10:40PM +0200, Orit Wasserman wrote:
>> 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
> 
> You are both right :). 64 looks like a sane value, and we can
> try and tune it some more if we have the time.
> 
Paolo, are you ok with leaving it MIN(IOV_MAX, 64) at the moment?
Later we can make it changeable.

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);
>>>>      }
>>>>  }
>>>>
>>>