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Date: Tue, 09 Apr 2013 15:22:23 +0300
From: Orit Wasserman <owasserm@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 4/4] migration: simplify writev vs.
	non-writev logic
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kwolf@redhat.com, qemu-devel@nongnu.org, quintela@redhat.com

On 04/09/2013 02:53 PM, Paolo Bonzini wrote:
> Il 09/04/2013 13:43, Juan Quintela ha scritto:
>>>> @@ -687,12 +685,10 @@ void qemu_put_byte(QEMUFile *f, int v)
>>>>      f->bytes_xfer++;
>>>>      if (f->ops->writev_buffer) {
>>>>          add_to_iovec(f, f->buf + f->buf_index, 1);
>>>> -        f->buf_index++;
>>>> -    } else {
>>>> -        f->buf_index++;
>>>> -        if (f->buf_index == IO_BUF_SIZE) {
>>>> -            qemu_fflush(f);
>>>> -        }
>>>> +    }
>>>> +    f->buf_index++;
>>>> +    if (f->buf_index == IO_BUF_SIZE) {
>>>> +        qemu_fflush(f);
>>>>      }
>>>>  }
>> If you follow my advice of moving the call to add_to_iovec() you get
>> this one simplified and only one place to do this.
> 
> Moving what call?  The apparent complication is because the old logic
> was a bit more involute than necessary.  If you look at the code after
> the patches, not the patches themselves, you'll see for yourself.
> 
> The logic now is:
> 
>    add byte
>    if using iovs
>        add byte to iov list
>    if buffer full
>        flush
> 
> add_to_iovec has no business checking the buffer.  Why should
> qemu_put_buffer_async() check the buffer?
> 
> The duplication between qemu_put_byte and qemu_put_buffer is a different
> topic.  I think it's acceptable in the name of performance, but perhaps
> you can just call qemu_put_buffer(f, &c, 1).
I thought about it too, we can keep the optimization by checking the size

Orit
> 
> Paolo
>