Re: [Qemu-devel] [PATCH v3 8/9] Use qemu_put_buffer_no_copy for guest memory pages

[Orit Wasserman <owasserm@redhat.com>]

On 03/21/2013 07:37 PM, Juan Quintela wrote:
> Orit Wasserman <owasserm@redhat.com> wrote:
>> This will remove an unneeded copy of guest memory pages.
>> For the page header and device state we still copy the data to the
>> static buffer the other option is to allocate the memory on demand
>> which is more expensive.
>>
>> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
>> ---
>>  arch_init.c | 2 +-
>>  savevm.c    | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch_init.c b/arch_init.c
>> index 98e2bc6..27b53eb 100644
>> --- a/arch_init.c
>> +++ b/arch_init.c
>> @@ -481,7 +481,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
>>              /* XBZRLE overflow or normal page */
>>              if (bytes_sent == -1) {
>>                  bytes_sent = save_block_hdr(f, block, offset, cont, RAM_SAVE_FLAG_PAGE);
>> -                qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
>> +                qemu_put_buffer_no_copy(f, p, TARGET_PAGE_SIZE);
>>                  bytes_sent += TARGET_PAGE_SIZE;
>>                  acct_info.norm_pages++;
>>              }
> 
> Once here, shouldn't we also change:
> 
> block-migration.c::blk_send()
> 
>     qemu_put_buffer(f, blk->buf, BLOCK_SIZE);
> 
> to nocopy?
Sadly no, I looked at the code and I saw the buffer is freed immediately
after call blk_send :(. look at mig_save_device_dirty.

Orit
> 
> Again, this can be an additional patch.
> 
> 
>> diff --git a/savevm.c b/savevm.c
>> index fbfb9e3..50e8fb2 100644
>> --- a/savevm.c
>> +++ b/savevm.c
>> @@ -634,7 +634,7 @@ void qemu_put_buffer_no_copy(QEMUFile *f, const uint8_t *buf, int size)
>>          abort();
>>      }
>>  
>> -    f->iov[f->iovcnt].iov_base = f->buf + f->buf_index;
>> +    f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
>>      f->iov[f->iovcnt++].iov_len = size;
> 
> This bit should be in the previous patch, the error that I pointed?
> 
> Later, Juan.
>