Re: [Qemu-devel] [QEMU 1/7] balloon: speed up inflating & deflating process

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

On Mon, Jun 13, 2016 at 06:16:43PM +0800, Liang Li 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 QEMU 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 210ms, it's about 8 times as fast as before.
> 
> TODO: optimize stage a by allocating/freeing a chunk of pages instead
> of a single page at a time.
> 
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> ---
>  hw/virtio/virtio-balloon.c                      | 159 ++++++++++++++++++++----
>  include/standard-headers/linux/virtio_balloon.h |   1 +
>  2 files changed, 139 insertions(+), 21 deletions(-)
> 
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 8c15e09..8cf74c2 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -47,6 +47,76 @@ static void balloon_page(void *addr, int deflate)
>  #endif
>  }
>  
> +static void do_balloon_bulk_pages(ram_addr_t base_pfn, int page_shift,
> +                                  unsigned long len, bool deflate)
> +{
> +    ram_addr_t size, processed, chunk, base;
> +    void *addr;
> +    MemoryRegionSection section = {.mr = NULL};
> +
> +    size = (len << page_shift);
> +    base = (base_pfn << page_shift);
> +
> +    for (processed = 0; processed < size; processed += chunk) {
> +        chunk = size - processed;
> +        while (chunk >= TARGET_PAGE_SIZE) {
> +            section = memory_region_find(get_system_memory(),
> +                                         base + processed, chunk);
> +            if (!section.mr) {
> +                chunk = QEMU_ALIGN_DOWN(chunk / 2, TARGET_PAGE_SIZE);
> +            } else {
> +                break;
> +            }
> +        }
> +
> +        if (section.mr &&
> +            (int128_nz(section.size) && memory_region_is_ram(section.mr))) {
> +            addr = section.offset_within_region +
> +                   memory_region_get_ram_ptr(section.mr);
> +            qemu_madvise(addr, chunk,
> +                         deflate ? QEMU_MADV_WILLNEED : QEMU_MADV_DONTNEED);
> +        } else {
> +            fprintf(stderr, "can't find the chunk, skip\n");
> +            chunk = TARGET_PAGE_SIZE;
> +        }
> +    }
> +}
> +
> +static void balloon_bulk_pages(ram_addr_t base_pfn, unsigned long *bitmap,
> +                               unsigned long len, int page_shift, bool deflate)
> +{
> +#if defined(__linux__)
> +    unsigned long end  = len * 8;
> +    unsigned long current = 0;
> +
> +    if (!qemu_balloon_is_inhibited() && (!kvm_enabled() ||
> +                                         kvm_has_sync_mmu())) {
> +        while (current < end) {
> +            unsigned long one = find_next_bit(bitmap, end, current);
> +
> +            if (one < end) {
> +                unsigned long zero = find_next_zero_bit(bitmap, end, one + 1);
> +                unsigned long page_length;
> +
> +                if (zero >= end) {
> +                    page_length = end - one;
> +                } else {
> +                    page_length = zero - one;
> +                }
> +
> +                if (page_length) {
> +                    do_balloon_bulk_pages(base_pfn + one, page_shift,
> +                                          page_length, deflate);
> +                }
> +                current = one + page_length;
> +            } else {
> +                current = one;
> +            }
> +        }
> +    }
> +#endif
> +}
> +
>  static const char *balloon_stat_names[] = {
>     [VIRTIO_BALLOON_S_SWAP_IN] = "stat-swap-in",
>     [VIRTIO_BALLOON_S_SWAP_OUT] = "stat-swap-out",
> @@ -78,6 +148,12 @@ static bool balloon_stats_supported(const VirtIOBalloon *s)
>      return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_STATS_VQ);
>  }
>  
> +static bool balloon_page_bitmap_supported(const VirtIOBalloon *s)
> +{
> +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> +    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> +}
> +
>  static bool balloon_stats_enabled(const VirtIOBalloon *s)
>  {
>      return s->stats_poll_interval > 0;
> @@ -224,27 +300,66 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>              return;
>          }
>  
> -        while (iov_to_buf(elem->out_sg, elem->out_num, offset, &pfn, 4) == 4) {
> -            ram_addr_t pa;
> -            ram_addr_t addr;
> -            int p = virtio_ldl_p(vdev, &pfn);
> -
> -            pa = (ram_addr_t) p << VIRTIO_BALLOON_PFN_SHIFT;
> -            offset += 4;
> -
> -            /* FIXME: remove get_system_memory(), but how? */
> -            section = memory_region_find(get_system_memory(), pa, 1);
> -            if (!int128_nz(section.size) || !memory_region_is_ram(section.mr))
> -                continue;
> -
> -            trace_virtio_balloon_handle_output(memory_region_name(section.mr),
> -                                               pa);
> -            /* Using memory_region_get_ram_ptr is bending the rules a bit, but
> -               should be OK because we only want a single page.  */
> -            addr = section.offset_within_region;
> -            balloon_page(memory_region_get_ram_ptr(section.mr) + addr,
> -                         !!(vq == s->dvq));
> -            memory_region_unref(section.mr);
> +        if (balloon_page_bitmap_supported(s)) {
> +            uint64_t base_pfn, tmp64, bmap_len;
> +            uint32_t tmp32, page_shift, id;
> +            unsigned long *bitmap;
> +
> +            iov_to_buf(elem->out_sg, elem->out_num, offset,
> +                       &tmp32, sizeof(uint32_t));
> +            id = virtio_ldl_p(vdev, &tmp32);
> +            offset += sizeof(uint32_t);
> +            /* to suppress build warning */
> +            id = id;
> +
> +            iov_to_buf(elem->out_sg, elem->out_num, offset,
> +                       &tmp32, sizeof(uint32_t));
> +            page_shift = virtio_ldl_p(vdev, &tmp32);
> +            offset += sizeof(uint32_t);
> +
> +            iov_to_buf(elem->out_sg, elem->out_num, offset,
> +                       &tmp64, sizeof(uint64_t));
> +            base_pfn = virtio_ldq_p(vdev, &tmp64);
> +            offset += sizeof(uint64_t);
> +
> +            iov_to_buf(elem->out_sg, elem->out_num, offset,
> +                       &tmp64, sizeof(uint64_t));
> +            bmap_len = virtio_ldq_p(vdev, &tmp64);
> +            offset += sizeof(uint64_t);
> +
> +            bitmap = bitmap_new(bmap_len * BITS_PER_BYTE);
> +            iov_to_buf(elem->out_sg, elem->out_num, offset,
> +                       bitmap, bmap_len);
> +            offset += bmap_len;
> +
> +            balloon_bulk_pages(base_pfn, bitmap, bmap_len,
> +                               page_shift, !!(vq == s->dvq));
> +            g_free(bitmap);
> +        } else {
> +            while (iov_to_buf(elem->out_sg, elem->out_num, offset,
> +                              &pfn, 4) == 4) {
> +                ram_addr_t pa;
> +                ram_addr_t addr;
> +                int p = virtio_ldl_p(vdev, &pfn);
> +
> +                pa = (ram_addr_t) p << VIRTIO_BALLOON_PFN_SHIFT;
> +                offset += 4;
> +
> +                /* FIXME: remove get_system_memory(), but how? */
> +                section = memory_region_find(get_system_memory(), pa, 1);
> +                if (!int128_nz(section.size) ||
> +                    !memory_region_is_ram(section.mr))
> +                    continue;
> +
> +                trace_virtio_balloon_handle_output(memory_region_name(
> +                                                            section.mr), pa);
> +                /* Using memory_region_get_ram_ptr is bending the rules a bit,
> +                 * but should be OK because we only want a single page.  */
> +                addr = section.offset_within_region;
> +                balloon_page(memory_region_get_ram_ptr(section.mr) + addr,
> +                             !!(vq == s->dvq));
> +                memory_region_unref(section.mr);
> +            }
>          }
>  
>          virtqueue_push(vq, elem, offset);
> @@ -374,6 +489,7 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
>      VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
>      f |= dev->host_features;
>      virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
> +    virtio_add_feature(&f, VIRTIO_BALLOON_F_PAGE_BITMAP);
>      return f;
>  }
>

Pls add features to virtio_balloon_properties.
You also need to handle compatibility by disabling for
old machine types.

  
> @@ -388,6 +504,7 @@ static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
>  {
>      VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
>      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> +
>      ram_addr_t vm_ram_size = get_current_ram_size();
>  
>      if (target > vm_ram_size) {
> diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
> index 9d06ccd..7c9686c 100644
> --- a/include/standard-headers/linux/virtio_balloon.h
> +++ b/include/standard-headers/linux/virtio_balloon.h
> @@ -34,6 +34,7 @@
>  #define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell before reclaiming pages */
>  #define VIRTIO_BALLOON_F_STATS_VQ	1 /* Memory Stats virtqueue */
>  #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate balloon on OOM */
> +#define VIRTIO_BALLOON_F_PAGE_BITMAP  3 /* Use page bitmap to send page info */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12

We want to keep this in sync with Linux.
Let's get a minimal patch to extend this header merged in linux, then update this one.

> -- 
> 1.9.1