From 920d557e5ae58671d335acbcfba3f9a97a02911c Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Tue, 18 Feb 2020 18:22:26 +0000 Subject: 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 Message-Id: <20200218182226.913977-1-stefanha@redhat.com> Signed-off-by: Paolo Bonzini --- memory.c | 18 +++++++++++++++--- 1 file 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; } -- cgit v1.2.3