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uio: Replace mutex info_lock with percpu_ref to improve performance 
This patch includes a modification to repace mutex info_lock with
percpu_ref, in order to improve uio performance.

Reviewed-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
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@guixinliu1995 @intel-lab-lkp
guixinliu1995 authored and intel-lab-lkp committed Feb 8, 2022
1 parent b86f329 commit 271c7d04f21a7c880e9dfb056eca51835576833d
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Showing 2 changed files with 75 additions and 25 deletions.
95 drivers/uio/uio.c
View file
@@ -24,6 +24,8 @@
#include <linux/kobject.h>
#include <linux/cdev.h>
#include <linux/uio_driver.h>
#include <linux/completion.h>
#include <linux/percpu-refcount.h>

#define UIO_MAX_DEVICES (1U << MINORBITS)

@@ -218,7 +220,9 @@ static ssize_t name_show(struct device *dev,
struct uio_device *idev = dev_get_drvdata(dev);
int ret;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (!idev->info) {
ret = -EINVAL;
dev_err(dev, "the device has been unregistered\n");
@@ -228,7 +232,7 @@ static ssize_t name_show(struct device *dev,
ret = sprintf(buf, "%s\n", idev->info->name);

out:
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
return ret;
}
static DEVICE_ATTR_RO(name);
@@ -239,7 +243,9 @@ static ssize_t version_show(struct device *dev,
struct uio_device *idev = dev_get_drvdata(dev);
int ret;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (!idev->info) {
ret = -EINVAL;
dev_err(dev, "the device has been unregistered\n");
@@ -249,7 +255,7 @@ static ssize_t version_show(struct device *dev,
ret = sprintf(buf, "%s\n", idev->info->version);

out:
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
return ret;
}
static DEVICE_ATTR_RO(version);
@@ -489,16 +495,20 @@ static int uio_open(struct inode *inode, struct file *filep)
listener->event_count = atomic_read(&idev->event);
filep->private_data = listener;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref)) {
ret = -EINVAL;
goto err_infoopen;
}

if (!idev->info) {
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
ret = -EINVAL;
goto err_infoopen;
}

if (idev->info->open)
ret = idev->info->open(idev->info, inode);
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
if (ret)
goto err_infoopen;

@@ -531,10 +541,12 @@ static int uio_release(struct inode *inode, struct file *filep)
struct uio_listener *listener = filep->private_data;
struct uio_device *idev = listener->dev;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (idev->info && idev->info->release)
ret = idev->info->release(idev->info, inode);
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);

module_put(idev->owner);
kfree(listener);
@@ -548,10 +560,12 @@ static __poll_t uio_poll(struct file *filep, poll_table *wait)
struct uio_device *idev = listener->dev;
__poll_t ret = 0;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (!idev->info || !idev->info->irq)
ret = -EIO;
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);

if (ret)
return ret;
@@ -577,13 +591,17 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
add_wait_queue(&idev->wait, &wait);

do {
mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref)) {
retval = -EINVAL;
break;
}

if (!idev->info || !idev->info->irq) {
retval = -EIO;
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
break;
}
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);

set_current_state(TASK_INTERRUPTIBLE);

@@ -631,7 +649,9 @@ static ssize_t uio_write(struct file *filep, const char __user *buf,
if (copy_from_user(&irq_on, buf, count))
return -EFAULT;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (!idev->info) {
retval = -EINVAL;
goto out;
@@ -650,7 +670,7 @@ static ssize_t uio_write(struct file *filep, const char __user *buf,
retval = idev->info->irqcontrol(idev->info, irq_on);

out:
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
return retval ? retval : sizeof(s32);
}

@@ -675,7 +695,9 @@ static vm_fault_t uio_vma_fault(struct vm_fault *vmf)
vm_fault_t ret = 0;
int mi;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (!idev->info) {
ret = VM_FAULT_SIGBUS;
goto out;
@@ -702,8 +724,7 @@ static vm_fault_t uio_vma_fault(struct vm_fault *vmf)
vmf->page = page;

out:
mutex_unlock(&idev->info_lock);

percpu_ref_put(&idev->info_ref);
return ret;
}

@@ -772,7 +793,9 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)

vma->vm_private_data = idev;

mutex_lock(&idev->info_lock);
if (!percpu_ref_tryget_live(&idev->info_ref))
return -EINVAL;

if (!idev->info) {
ret = -EINVAL;
goto out;
@@ -811,7 +834,7 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
}

out:
mutex_unlock(&idev->info_lock);
percpu_ref_put(&idev->info_ref);
return ret;
}

@@ -907,6 +930,13 @@ static void uio_device_release(struct device *dev)
kfree(idev);
}

static void uio_info_free(struct percpu_ref *ref)
{
struct uio_device *idev = container_of(ref, struct uio_device, info_ref);

complete(&idev->free_done);
}

/**
* __uio_register_device - register a new userspace IO device
* @owner: module that creates the new device
@@ -937,10 +967,17 @@ int __uio_register_device(struct module *owner,

idev->owner = owner;
idev->info = info;
mutex_init(&idev->info_lock);
init_waitqueue_head(&idev->wait);
atomic_set(&idev->event, 0);

ret = percpu_ref_init(&idev->info_ref, uio_info_free, 0, GFP_KERNEL);
if (ret) {
pr_err("percpu_ref init failed!\n");
return ret;
}
init_completion(&idev->confirm_done);
init_completion(&idev->free_done);

ret = uio_get_minor(idev);
if (ret) {
kfree(idev);
@@ -1036,6 +1073,13 @@ int __devm_uio_register_device(struct module *owner,
}
EXPORT_SYMBOL_GPL(__devm_uio_register_device);

static void uio_confirm_info(struct percpu_ref *ref)
{
struct uio_device *idev = container_of(ref, struct uio_device, info_ref);

complete(&idev->confirm_done);
}

/**
* uio_unregister_device - unregister a industrial IO device
* @info: UIO device capabilities
@@ -1052,14 +1096,17 @@ void uio_unregister_device(struct uio_info *info)
idev = info->uio_dev;
minor = idev->minor;

mutex_lock(&idev->info_lock);
percpu_ref_kill_and_confirm(&idev->info_ref, uio_confirm_info);
wait_for_completion(&idev->confirm_done);
wait_for_completion(&idev->free_done);

/* now, we can set info to NULL */
uio_dev_del_attributes(idev);

if (info->irq && info->irq != UIO_IRQ_CUSTOM)
free_irq(info->irq, idev);

idev->info = NULL;
mutex_unlock(&idev->info_lock);

wake_up_interruptible(&idev->wait);
kill_fasync(&idev->async_queue, SIGIO, POLL_HUP);
5 include/linux/uio_driver.h
View file
@@ -16,6 +16,7 @@
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/interrupt.h>
#include <linux/percpu-refcount.h>

struct module;
struct uio_map;
@@ -74,9 +75,11 @@ struct uio_device {
struct fasync_struct *async_queue;
wait_queue_head_t wait;
struct uio_info *info;
struct mutex info_lock;
struct kobject *map_dir;
struct kobject *portio_dir;
struct percpu_ref info_ref;
struct completion confirm_done;
struct completion free_done;
};

/**

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