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Date: Thu, 21 Mar 2013 18:27:42 +0200
From: Orit Wasserman <owasserm@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 9/9] coalesce adjacent iovecs
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: pbonzini@redhat.com, chegu_vinod@hp.com, qemu-devel@nongnu.org, quintela@redhat.com

On 03/21/2013 06:16 PM, Michael S. Tsirkin wrote:
> On Thu, Mar 21, 2013 at 06:05:40PM +0200, Orit Wasserman wrote:
>> This way we send one big buffer instead of many small ones
>>
>> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
> 
> Why does this happen BTW?

It happens in the last phase when we send the device state that consists of a lot
bytes and int field that are written using qemu_put_byte/be16/...


> 
>> ---
>>  savevm.c | 21 +++++++++++++++++----
>>  1 file changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/savevm.c b/savevm.c
>> index 50e8fb2..13a533b 100644
>> --- a/savevm.c
>> +++ b/savevm.c
>> @@ -634,8 +634,14 @@ void qemu_put_buffer_no_copy(QEMUFile *f, const uint8_t *buf, int size)
>>          abort();
>>      }
>>  
>> -    f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
>> -    f->iov[f->iovcnt++].iov_len = size;
>> +    /* check for adjoint buffer and colace them */
>> +    if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
>> +        f->iov[f->iovcnt - 1].iov_len) {
>> +        f->iov[f->iovcnt - 1].iov_len += size;
>> +    } else {
>> +        f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
>> +        f->iov[f->iovcnt++].iov_len = size;
>> +    }
>>  
>>      f->is_write = 1;
>>      f->bytes_xfer += size;
>> @@ -690,8 +696,15 @@ 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;
>> +
>> +    /* check for adjoint buffer and colace them */
>> +    if (f->iovcnt > 0 && f->buf + (f->buf_index - 1)  ==
>> +        f->iov[f->iovcnt - 1].iov_base + f->iov[f->iovcnt - 1].iov_len) {
>> +        f->iov[f->iovcnt - 1].iov_len += 1;
>> +    } else {
>> +        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 || f->iovcnt >= MAX_IOV_SIZE) {
>>          qemu_fflush(f);
>> -- 
>> 1.7.11.7