[PATCH] pci: call _cond_resched() after pci_bus_write_config

[menglong8 . dong]

From: Menglong Dong <imagedong@xxxxxxxxxxx>

While the system is running in KVM, pci config writing for virtio devices
may cost long time(about 1-2ms), as it causes VM-exit. During
__pci_bus_assign_resources(), pci_setup_bridge, which can do pci config
writing up to 10 times, can be called many times without any
_cond_resched(). So __pci_bus_assign_resources can cause 25+ms scheduling
latency with !CONFIG_PREEMPT.

To solve this problem, call _cond_resched() after pci config writing.

Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
---
 drivers/pci/access.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 46935695cfb9..babed43702df 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -57,6 +57,7 @@ int noinline pci_bus_write_config_##size \
 	pci_lock_config(flags);						\
 	res = bus->ops->write(bus, devfn, pos, len, value);		\
 	pci_unlock_config(flags);					\
+	_cond_resched();						\
 	return res;							\
 }
 
-- 
2.27.0