[PATCH 2/2] pci: load a device's config inside one memory transaction

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

Restoring config space remaps the BARs, updates the bridge windows when
the device is a bridge, and toggles the bus master region. Each of those
commits a transaction of its own, so one device costs several flatview
rebuilds where one would do, and the cost of a rebuild grows with the
number of regions in the machine.

Nothing between them touches an address space, so the three can share a
transaction. The saving scales with the number of PCI devices.

CC: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Denis V. Lunev <den@virtuozzo.com>
---
 hw/pci/pci.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 14c78e3c62..0efb4eb4bb 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -840,6 +840,8 @@ static int get_pci_config_device(QEMUFile *f, void *pv, size_t size,
     }
     memcpy(s->config, config, size);
 
+    memory_region_transaction_begin();
+
     pci_update_mappings(s);
     if (IS_PCI_BRIDGE(s)) {
         pci_bridge_update_mappings(PCI_BRIDGE(s));
@@ -848,6 +850,8 @@ static int get_pci_config_device(QEMUFile *f, void *pv, size_t size,
     pci_set_master(s, pci_get_word(s->config + PCI_COMMAND)
                       & PCI_COMMAND_MASTER);
 
+    memory_region_transaction_commit();
+
     g_free(config);
     return 0;
 }
-- 
2.53.0