Re: [Qemu-devel] [virtio-dev] Re: [PATCH v7 kernel 3/5] virtio-balloon: implementation of VIRTIO_BALLOON_F_CHUNK_TRANSFER

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Mar 10, 2017 at 06:02:31PM +0800, Wei Wang wrote:
> On 03/08/2017 12:01 PM, Michael S. Tsirkin wrote:
> > On Fri, Mar 03, 2017 at 01:40:28PM +0800, Wei Wang wrote:
> > > From: Liang Li <liang.z.li@intel.com>
> > > 
> > > The implementation of the current virtio-balloon is not very
> > > efficient, because the pages are transferred to the host one by one.
> > > Here is the breakdown of the time in percentage spent on each
> > > step of the balloon inflating process (inflating 7GB of an 8GB
> > > idle guest).
> > > 
> > > 1) allocating pages (6.5%)
> > > 2) sending PFNs to host (68.3%)
> > > 3) address translation (6.1%)
> > > 4) madvise (19%)
> > > 
> > > It takes about 4126ms for the inflating process to complete.
> > > The above profiling shows that the bottlenecks are stage 2)
> > > and stage 4).
> > > 
> > > This patch optimizes step 2) by transfering pages to the host in
> > > chunks. A chunk consists of guest physically continuous pages, and
> > > it is offered to the host via a base PFN (i.e. the start PFN of
> > > those physically continuous pages) and the size (i.e. the total
> > > number of the pages). A normal chunk is formated as below:
> > > -----------------------------------------------
> > > |  Base (52 bit)               | Size (12 bit)|
> > > -----------------------------------------------
> > > For large size chunks, an extended chunk format is used:
> > > -----------------------------------------------
> > > |                 Base (64 bit)               |
> > > -----------------------------------------------
> > > -----------------------------------------------
> > > |                 Size (64 bit)               |
> > > -----------------------------------------------
> > > 
> > > By doing so, step 4) can also be optimized by doing address
> > > translation and madvise() in chunks rather than page by page.
> > > 
> > > This optimization requires the negotation of a new feature bit,
> > > VIRTIO_BALLOON_F_CHUNK_TRANSFER.
> > > 
> > > With this new feature, the above ballooning process takes ~590ms
> > > resulting in an improvement of ~85%.
> > > 
> > > TODO: optimize stage 1) by allocating/freeing a chunk of pages
> > > instead of a single page each time.
> > > 
> > > Signed-off-by: Liang Li <liang.z.li@intel.com>
> > > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > > Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > > Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> > > Cc: Amit Shah <amit.shah@redhat.com>
> > > Cc: Dave Hansen <dave.hansen@intel.com>
> > > Cc: Andrea Arcangeli <aarcange@redhat.com>
> > > Cc: David Hildenbrand <david@redhat.com>
> > > Cc: Liang Li <liliang324@gmail.com>
> > > Cc: Wei Wang <wei.w.wang@intel.com>
> > Does this pass sparse? I see some endian-ness issues here.
> 
> "pass sparse"- what does that mean?
> I didn't see any complaints from "make" on my machine.


Run with make C=1 (or C=2 to check all source).

Generally there's a ton of useful info you will find
if you run make help.

-- 
MST