The implementation of the current virtio-balloon is not very
efficient, the time spends on different stages of inflating
the balloon to 7GB of a 8GB idle guest:
a. allocating pages (6.5%)
b. sending PFNs to host (68.3%)
c. address translation (6.1%)
d. madvise (19%)
It takes about 4126ms for the inflating process to complete.
Debugging shows that the bottle neck are the stage b and stage d.
If using a bitmap to send the page info instead of the PFNs, we
can reduce the overhead in stage b quite a lot. Furthermore, we
can do the address translation and call madvise() with a bulk of
RAM pages, instead of the current page per page way, 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. With this new feature, inflating the
balloon to 7GB of a 8GB idle guest only takes 590ms, the
performance improvement is about 85%.
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@xxxxxxxxx>
Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
hw/virtio/virtio-balloon.c | 144 ++++++++++++++++++++++++++++++++++++++-------
1 file changed, 123 insertions(+), 21 deletions(-)
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 1d77028..3fa80a4 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -52,6 +52,77 @@ static const char *balloon_stat_names[] = {
[VIRTIO_BALLOON_S_NR] = NULL
};
+static void do_balloon_bulk_pages(ram_addr_t base_pfn, uint16_t page_shift,
+ unsigned long len, bool deflate)
+{
+ ram_addr_t size, processed, chunk, base;
+ 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))) {
+ void *addr = section.offset_within_region +
+ memory_region_get_ram_ptr(section.mr);
+ qemu_madvise(addr, chunk,
+ deflate ? QEMU_MADV_WILLNEED : QEMU_MADV_DONTNEED);
+ } else {
+ qemu_log_mask(LOG_GUEST_ERROR,
+ "Invalid guest RAM range [0x%lx, 0x%lx]\n",
+ base + processed, chunk);
+ chunk = TARGET_PAGE_SIZE;
+ }
+ }
+}
+
+static void balloon_bulk_pages(struct balloon_bmap_hdr *hdr,
+ unsigned long *bitmap, bool deflate)
+{
+ ram_addr_t base_pfn = hdr->start_pfn;
+ uint16_t page_shift = hdr->page_shift;
+ unsigned long len = hdr->bmap_len;
+ unsigned long current = 0, end = len * BITS_PER_BYTE;
+
+ 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 pages, zero;
+
+ zero = find_next_zero_bit(bitmap, end, one + 1);
+ if (zero >= end) {
+ pages = end - one;
+ } else {
+ pages = zero - one;
+ }
+
+ if (pages) {
+ do_balloon_bulk_pages(base_pfn + one, page_shift,
+ pages, deflate);
+ }
+ current = one + pages;
+ } else {
+ current = one;
+ }
+ }
+ }
+}
+
/*
* reset_stats - Mark all items in the stats array as unset
*
@@ -72,6 +143,13 @@ 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;
@@ -213,32 +291,54 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
for (;;) {
size_t offset = 0;
uint32_t pfn;
+
elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
if (!elem) {
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)) {
+ struct balloon_bmap_hdr hdr;
+ uint64_t bmap_len;
+
+ iov_to_buf(elem->out_sg, elem->out_num, offset, &hdr, sizeof(hdr));
+ offset += sizeof(hdr);
+
+ bmap_len = hdr.bmap_len;
+ if (bmap_len > 0) {
+ unsigned long *bitmap = bitmap_new(bmap_len * BITS_PER_BYTE);
+ iov_to_buf(elem->out_sg, elem->out_num, offset,
+ bitmap, bmap_len);
+
+ balloon_bulk_pages(&hdr, bitmap, !!(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);
@@ -500,6 +600,8 @@ static const VMStateDescription vmstate_virtio_balloon = {
static Property virtio_balloon_properties[] = {
DEFINE_PROP_BIT("deflate-on-oom", VirtIOBalloon, host_features,
VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
+ DEFINE_PROP_BIT("page-bitmap", VirtIOBalloon, host_features,
+ VIRTIO_BALLOON_F_PAGE_BITMAP, true),
DEFINE_PROP_END_OF_LIST(),
};
--
1.8.3.1
--
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