Re: [Qemu-devel] [PATCH 0/6] migration: differentiate between pages and bytes

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Li, Liang Z (liang.z.li@intel.com) wrote:
> 
> 
> > -----Original Message-----
> > From: Dr. David Alan Gilbert [mailto:dgilbert@redhat.com]
> > Sent: Tuesday, February 17, 2015 10:24 PM
> > To: Juan Quintela
> > Cc: qemu-devel@nongnu.org; Li, Liang Z
> > Subject: Re: [Qemu-devel] [PATCH 0/6] migration: differentiate between
> > pages and bytes
> > 
> > * Juan Quintela (quintela@redhat.com) wrote:
> > > Hi
> > >
> > > (Li special edition)
> > >
> > > Current migration code returns number of bytes transferred and from
> > > there we decide if we.have sent something or not.  Problem, we need
> > > two results: number of pages written, and number of bytes written
> > > (depending on compression, zero pages, etc, it is not possible to
> > > derive one value from the other).
> > >
> > > So, I changed all relevant function to return the number of written
> > > pages, and then pass as uint64_t *bytes_transferred to update the
> > > written bytes.
> > >
> > > On current code, makes things a bit easier to understand, but is not
> > > strictely necesary.  But for the compression patches from Li, it makes
> > > a big difference, we can return that we have written a page, even if
> > > we have just started the write, but having writtten in reality zero
> > > bytes.
> > >
> > > Once there, I add doxygen documentation to all function that I touched
> > > (yes, I was long due).
> > >
> > > save_block_hdr really saved headers for pages, not blocks.  Rename it,
> > > and simplify the interface.
> > >
> > > Li, does this make your life easier?  I hope so.  Should make really
> > > easy to remove the one_bytes_sent "hack", and allow my other
> > suggestions.
> > >
> > > Comments?
> > 
> > I like it; it generally seems to make sense to separate the concept of whether
> > we've actually sent any pages from the actual byte counting.
> > 
> > While you're there though; do we actually care about bean counting the
> > individual header bytes?  For example the &bytes_transferred += 1 in the
> > RAM_SAVE_FLAG_COMPRESS case where it puts the 0, or the EOS mark
> > where
> > we add 8 bytes?   Do we need to keep track of anything other than
> > stuff that's potentially big enough to make an impact on the bandwidth
> > calculations?
> > 
> 
> Can pos of QEMUFile be used to counting the transferred bytes ?

I think we probably can.

Dave

> Liang
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK