> On Fri, 20 May 2016 17:59:46 +0800
> Liang Li <liang.z.li@xxxxxxxxx> wrote:
>
> > The implementation of the current virtio-balloon is not very
> > efficient, Bellow is test result of time spends on inflating the
> > balloon to 3GB of a 4GB idle guest:
> >
> > a. allocating pages (6.5%, 103ms)
> > b. sending PFNs to host (68.3%, 787ms) c. address translation (6.1%,
> > 96ms) d. madvise (19%, 300ms)
> >
> > It takes about 1577ms for the whole inflating process to complete. The
> > test shows that the bottle neck is the stage b and stage d.
> >
> > If using a bitmap to send the page info instead of the PFNs, we can
> > reduce the overhead spends on stage b quite a lot. Furthermore, it's
> > possible to do the address translation and do the madvise with a bulk
> > of pages, instead of the current page per page way, so the overhead of
> > stage c and stage d can also be reduced a lot.
> >
> > This patch is the kernel side implementation which is intended to
> > speed up the inflating & deflating process by adding a new feature to
> > the virtio-balloon device. And now, inflating the balloon to 3GB of a
> > 4GB idle guest only takes 175ms, it's about 9 times as fast as before.
> >
> > TODO: optimize stage a by allocating/freeing a chunk of pages instead
> > of a single page at a time.
>
> Not commenting on the approach, but...
>
> >
> > Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> > ---
> > drivers/virtio/virtio_balloon.c | 199
> ++++++++++++++++++++++++++++++++++--
> > include/uapi/linux/virtio_balloon.h | 1 +
> > mm/page_alloc.c | 6 ++
> > 3 files changed, 198 insertions(+), 8 deletions(-)
> >
>
> > static void tell_host(struct virtio_balloon *vb, struct virtqueue
> > *vq) {
> > - struct scatterlist sg;
> > unsigned int len;
> >
> > - sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
> > + if (virtio_has_feature(vb->vdev,
> VIRTIO_BALLOON_F_PAGE_BITMAP)) {
> > + u32 page_shift = PAGE_SHIFT;
> > + unsigned long start_pfn, end_pfn, flags = 0, bmap_len;
> > + struct scatterlist sg[5];
> > +
> > + start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> > + end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> > + bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG *
> sizeof(long);
> > +
> > + sg_init_table(sg, 5);
> > + sg_set_buf(&sg[0], &flags, sizeof(flags));
> > + sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn));
> > + sg_set_buf(&sg[2], &page_shift, sizeof(page_shift));
> > + sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
> > + sg_set_buf(&sg[4], vb->page_bitmap +
> > + (start_pfn / BITS_PER_LONG), bmap_len);
> > + virtqueue_add_outbuf(vq, sg, 5, vb, GFP_KERNEL);
> > +
>
> ...you need to take care of the endianness of the data you put on the queue,
> otherwise virtio-1 on big endian won't work. (There's just been a patch for
> that problem.)
OK, thanks for your reminding.
Liang
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