PCI: Sleep rather than busy-wait for VPD access completion
Use usleep_range() instead of udelay() while waiting for a VPD access to
complete. This is not a performance path, so no need to hog the CPU.
Rationale for usleep_range() parameters:
We clear PCI_VPD_ADDR_F for a read (or set it for a write), then wait for
the device to change it. For a device that updates PCI_VPD_ADDR between
our config write and subsequent config read, we won't sleep at all and
can get the device's maximum rate.
Sleeping a minimum of 10 usec per 4-byte access limits throughput to
about 400Kbytes/second. VPD is small (32K bytes at most), and most
devices use only a fraction of that.
We back off exponentially up to 1024 usec per iteration. If we reach
1024, we've already waited up to 1008 usec (16 + 32 + ... + 512), so if
we miss an update and wait an extra 1024 usec, we can still get about
1/2 of the device's maximum rate.
Tested-by: Shane Seymour <shane.seymour@hpe.com>
Tested-by: Babu Moger <babu.moger@oracle.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 8449d6b5..01b9d0a 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -342,14 +342,15 @@
static int pci_vpd_wait(struct pci_dev *dev)
{
struct pci_vpd *vpd = dev->vpd;
- unsigned long timeout = jiffies + HZ/20 + 2;
+ unsigned long timeout = jiffies + msecs_to_jiffies(50);
+ unsigned long max_sleep = 16;
u16 status;
int ret;
if (!vpd->busy)
return 0;
- for (;;) {
+ while (time_before(jiffies, timeout)) {
ret = pci_user_read_config_word(dev, vpd->cap + PCI_VPD_ADDR,
&status);
if (ret < 0)
@@ -360,15 +361,16 @@
return 0;
}
- if (time_after(jiffies, timeout)) {
- dev_printk(KERN_DEBUG, &dev->dev, "vpd r/w failed. This is likely a firmware bug on this device. Contact the card vendor for a firmware update\n");
- return -ETIMEDOUT;
- }
if (fatal_signal_pending(current))
return -EINTR;
- if (!cond_resched())
- udelay(10);
+
+ usleep_range(10, max_sleep);
+ if (max_sleep < 1024)
+ max_sleep *= 2;
}
+
+ dev_warn(&dev->dev, "VPD access failed. This is likely a firmware bug on this device. Contact the card vendor for a firmware update\n");
+ return -ETIMEDOUT;
}
static ssize_t pci_vpd_read(struct pci_dev *dev, loff_t pos, size_t count,
