[PATCH] PCI: optimize proc sequential file read

Guixin Liu
2024-10-18T05:47:43Z

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