diff options
author | Alexey Kardashevskiy <aik@ozlabs.ru> | 2017-09-21 18:51:07 +1000 |
---|---|---|
committer | Michael Roth <mdroth@linux.vnet.ibm.com> | 2017-12-04 22:42:02 -0600 |
commit | 496f97293e29361f48054f63adcbf1187c99fca2 (patch) | |
tree | dd9ffe17a944e5bf48942ecf43abcf3f39414ec2 | |
parent | 639701e4f2f57cd54b657a8281dba72d067db8ee (diff) | |
download | qemu-496f97293e29361f48054f63adcbf1187c99fca2.tar.gz |
memory: Share special empty FlatView
This shares an cached empty FlatView among address spaces. The empty
FV is used every time when a root MR renders into a FV without memory
sections which happens when MR or its children are not enabled or
zero-sized. The empty_view is not NULL to keep the rest of memory
API intact; it also has a dispatch tree for the same reason.
On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves
the amount of FlatView's in use (557 -> 260) and dispatch tables
(~800000 -> ~370000). In an unrelated experiment with 112 non-virtio
devices on x86 ("-M pc"), only 4 FlatViews are alive, and about ~2000
are created at startup.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20170921085110.25598-16-aik@ozlabs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 092aa2fc65b7a35121616aad8f39d47b8f921618)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
-rw-r--r-- | memory.c | 18 |
1 files changed, 16 insertions, 2 deletions
@@ -317,6 +317,7 @@ static void flatview_unref(FlatView *view) { if (atomic_fetch_dec(&view->ref) == 1) { trace_flatview_destroy_rcu(view, view->root); + assert(view->root); call_rcu(view, flatview_destroy, rcu); } } @@ -760,16 +761,19 @@ static MemoryRegion *memory_region_get_flatview_root(MemoryRegion *mr) } } } + if (found == 0) { + return NULL; + } if (next) { mr = next; continue; } } - break; + return mr; } - return mr; + return NULL; } /* Render a memory topology into a list of disjoint absolute ranges. */ @@ -965,12 +969,22 @@ static void address_space_update_topology_pass(AddressSpace *as, static void flatviews_init(void) { + static FlatView *empty_view; + if (flat_views) { return; } flat_views = g_hash_table_new_full(g_direct_hash, g_direct_equal, NULL, (GDestroyNotify) flatview_unref); + if (!empty_view) { + empty_view = generate_memory_topology(NULL); + /* We keep it alive forever in the global variable. */ + flatview_ref(empty_view); + } else { + g_hash_table_replace(flat_views, NULL, empty_view); + flatview_ref(empty_view); + } } static void flatviews_reset(void) |