From: Jiang Biao <benbjiang@xxxxxxxxxxx>
pci_read_config() could block several ms in kernel space, mainly
caused by the while loop to call pci_user_read_config_dword().
Singel pci_user_read_config_dword() loop could consume 130us+,
| pci_user_read_config_dword() {
| _raw_spin_lock_irq() {
! 136.698 us | native_queued_spin_lock_slowpath();
! 137.582 us | }
| pci_read() {
| raw_pci_read() {
| pci_conf1_read() {
0.230 us | _raw_spin_lock_irqsave();
0.035 us | _raw_spin_unlock_irqrestore();
8.476 us | }
8.790 us | }
9.091 us | }
! 147.263 us | }
and dozens of the loop could consume ms+.
If we execute some lspci commands concurrently, ms+ scheduling
latency could be detected.
Add scheduling chance in the loop to improve the latency.
Reported-by: Bin Lai <robinlai@xxxxxxxxxxx>
Signed-off-by: Jiang Biao <benbjiang@xxxxxxxxxxx>
---
drivers/pci/pci-sysfs.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 6d78df9..3b9f63d 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -708,6 +708,7 @@ static ssize_t pci_read_config(struct file *filp, struct kobject *kobj,
data[off - init_off + 3] = (val >> 24) & 0xff;
off += 4;
size -= 4;
+ cond_resched();
}
if (size >= 2) {
--
1.8.3.1
