[PATCH] PCI: optimize proc sequential file read

[Guixin Liu <kanie@linux.alibaba.com>]

PCI driver will traverse pci device list in pci_seq_start in every
sequential file reading, use xarry to store all pci devices to
accelerate finding the start.

Use "time cat /proc/bus/pci/devices" to test on a machine with 13k
pci devices,  get an increase of about 90%.

Without this patch:
  real 0m0.917s
  user 0m0.000s
  sys  0m0.913s
With this patch:
  real 0m0.093s
  user 0m0.000s
  sys  0m0.093s

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---
 drivers/pci/pci.h    |  3 +++
 drivers/pci/probe.c  |  1 +
 drivers/pci/proc.c   | 64 +++++++++++++++++++++++++++++++++++++++-----
 drivers/pci/remove.c |  1 +
 include/linux/pci.h  |  2 ++
 5 files changed, 64 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 14d00ce45bfa..1a7da91eeb80 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -962,4 +962,7 @@ void pcim_release_region(struct pci_dev *pdev, int bar);
 	(PCI_CONF1_ADDRESS(bus, dev, func, reg) | \
 	 PCI_CONF1_EXT_REG(reg))
 
+void pci_seq_tree_add_dev(struct pci_dev *dev);
+void pci_seq_tree_remove_dev(struct pci_dev *dev);
+
 #endif /* DRIVERS_PCI_H */
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4f68414c3086..1fd9e9022f70 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2592,6 +2592,7 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
 	WARN_ON(ret < 0);
 
 	pci_npem_create(dev);
+	pci_seq_tree_add_dev(dev);
 }
 
 struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index f967709082d6..30ca071ccad5 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -19,6 +19,9 @@
 
 static int proc_initialized;	/* = 0 */
 
+DEFINE_XARRAY_FLAGS(pci_seq_tree, 0);
+static unsigned long pci_max_idx;
+
 static loff_t proc_bus_pci_lseek(struct file *file, loff_t off, int whence)
 {
 	struct pci_dev *dev = pde_data(file_inode(file));
@@ -334,25 +337,72 @@ static const struct proc_ops proc_bus_pci_ops = {
 #endif /* HAVE_PCI_MMAP */
 };
 
+void pci_seq_tree_add_dev(struct pci_dev *dev)
+{
+	int ret;
+
+	if (dev) {
+		xa_lock(&pci_seq_tree);
+		pci_dev_get(dev);
+		ret = __xa_insert(&pci_seq_tree, pci_max_idx, dev, GFP_KERNEL);
+		if (!ret) {
+			dev->proc_seq_idx = pci_max_idx;
+			pci_max_idx++;
+		} else {
+			pci_dev_put(dev);
+			WARN_ON(ret);
+		}
+		xa_unlock(&pci_seq_tree);
+	}
+}
+
+void pci_seq_tree_remove_dev(struct pci_dev *dev)
+{
+	unsigned long idx = dev->proc_seq_idx;
+	struct pci_dev *latest_dev = NULL;
+	struct pci_dev *ret;
+
+	if (!dev)
+		return;
+
+	xa_lock(&pci_seq_tree);
+	__xa_erase(&pci_seq_tree, idx);
+	pci_dev_put(dev);
+	/*
+	 * Move the latest pci_dev to this idx to keep the continuity.
+	 */
+	if (idx != pci_max_idx - 1) {
+		latest_dev = __xa_erase(&pci_seq_tree, pci_max_idx - 1);
+		ret = __xa_cmpxchg(&pci_seq_tree, idx, NULL, latest_dev,
+				GFP_KERNEL);
+		if (!ret)
+			latest_dev->proc_seq_idx = idx;
+		WARN_ON(ret);
+	}
+	pci_max_idx--;
+	xa_unlock(&pci_seq_tree);
+}
+
 /* iterator */
 static void *pci_seq_start(struct seq_file *m, loff_t *pos)
 {
-	struct pci_dev *dev = NULL;
+	struct pci_dev *dev;
 	loff_t n = *pos;
 
-	for_each_pci_dev(dev) {
-		if (!n--)
-			break;
-	}
+	dev = xa_load(&pci_seq_tree, n);
+	if (dev)
+		pci_dev_get(dev);
 	return dev;
 }
 
 static void *pci_seq_next(struct seq_file *m, void *v, loff_t *pos)
 {
-	struct pci_dev *dev = v;
+	struct pci_dev *dev;
 
 	(*pos)++;
-	dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, dev);
+	dev = xa_load(&pci_seq_tree, *pos);
+	if (dev)
+		pci_dev_get(dev);
 	return dev;
 }
 
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index e4ce1145aa3e..257ea46233a3 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -53,6 +53,7 @@ static void pci_destroy_dev(struct pci_dev *dev)
 	pci_npem_remove(dev);
 
 	device_del(&dev->dev);
+	pci_seq_tree_remove_dev(dev);
 
 	down_write(&pci_bus_sem);
 	list_del(&dev->bus_list);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 573b4c4c2be6..aeb3d4cce06a 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -534,6 +534,8 @@ struct pci_dev {
 
 	/* These methods index pci_reset_fn_methods[] */
 	u8 reset_methods[PCI_NUM_RESET_METHODS]; /* In priority order */
+
+	unsigned long long	proc_seq_idx;
 };
 
 static inline struct pci_dev *pci_physfn(struct pci_dev *dev)
-- 
2.43.0