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authorStefan Hajnoczi <stefanha@redhat.com>2020-02-18 18:22:26 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2020-02-25 09:18:01 +0100
commit920d557e5ae58671d335acbcfba3f9a97a02911c (patch)
treec6fbdce4ebcffb29ae5f92322b2e82ebc7216a09
parentc1e667d2598b9b3ce62b8e89ed22dd38dfe9f57f (diff)
downloadqemu-arm-920d557e5ae58671d335acbcfba3f9a97a02911c.tar.gz
memory: batch allocate ioeventfds[] in address_space_update_ioeventfds()
Reallocing the ioeventfds[] array each time an element is added is very expensive as the number of ioeventfds increases. Batch allocate instead to amortize the cost of realloc. This patch reduces Linux guest boot times from 362s to 140s when there are 2 virtio-blk devices with 1 virtqueue and 99 virtio-blk devices with 32 virtqueues. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Message-Id: <20200218182226.913977-1-stefanha@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--memory.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/memory.c b/memory.c
index aeaa8dcc9e..09be40edd2 100644
--- a/memory.c
+++ b/memory.c
@@ -794,10 +794,19 @@ static void address_space_update_ioeventfds(AddressSpace *as)
FlatView *view;
FlatRange *fr;
unsigned ioeventfd_nb = 0;
- MemoryRegionIoeventfd *ioeventfds = NULL;
+ unsigned ioeventfd_max;
+ MemoryRegionIoeventfd *ioeventfds;
AddrRange tmp;
unsigned i;
+ /*
+ * It is likely that the number of ioeventfds hasn't changed much, so use
+ * the previous size as the starting value, with some headroom to avoid
+ * gratuitous reallocations.
+ */
+ ioeventfd_max = QEMU_ALIGN_UP(as->ioeventfd_nb, 4);
+ ioeventfds = g_new(MemoryRegionIoeventfd, ioeventfd_max);
+
view = address_space_get_flatview(as);
FOR_EACH_FLAT_RANGE(fr, view) {
for (i = 0; i < fr->mr->ioeventfd_nb; ++i) {
@@ -806,8 +815,11 @@ static void address_space_update_ioeventfds(AddressSpace *as)
int128_make64(fr->offset_in_region)));
if (addrrange_intersects(fr->addr, tmp)) {
++ioeventfd_nb;
- ioeventfds = g_realloc(ioeventfds,
- ioeventfd_nb * sizeof(*ioeventfds));
+ if (ioeventfd_nb > ioeventfd_max) {
+ ioeventfd_max = MAX(ioeventfd_max * 2, 4);
+ ioeventfds = g_realloc(ioeventfds,
+ ioeventfd_max * sizeof(*ioeventfds));
+ }
ioeventfds[ioeventfd_nb-1] = fr->mr->ioeventfds[i];
ioeventfds[ioeventfd_nb-1].addr = tmp;
}