linux/drivers/android/binder_alloc.h
Carlos Llamas 7710e2cca3 binder: switch alloc->mutex to spinlock_t
The alloc->mutex is a highly contended lock that causes performance
issues on Android devices. When a low-priority task is given this lock
and it sleeps, it becomes difficult for the task to wake up and complete
its work. This delays other tasks that are also waiting on the mutex.

The problem gets worse when there is memory pressure in the system,
because this increases the contention on the alloc->mutex while the
shrinker reclaims binder pages.

Switching to a spinlock helps to keep the waiters running and avoids the
overhead of waking up tasks. This significantly improves the transaction
latency when the problematic scenario occurs.

The performance impact of this patchset was measured by stress-testing
the binder alloc contention. In this test, several clients of different
priorities send thousands of transactions of different sizes to a single
server. In parallel, pages get reclaimed using the shinker's debugfs.

The test was run on a Pixel 8, Pixel 6 and qemu machine. The results
were similar on all three devices:

after:
  | sched  | prio | average | max       | min     |
  |--------+------+---------+-----------+---------|
  | fifo   |   99 | 0.135ms |   1.197ms | 0.022ms |
  | fifo   |   01 | 0.136ms |   5.232ms | 0.018ms |
  | other  |  -20 | 0.180ms |   7.403ms | 0.019ms |
  | other  |   19 | 0.241ms |  58.094ms | 0.018ms |

before:
  | sched  | prio | average | max       | min     |
  |--------+------+---------+-----------+---------|
  | fifo   |   99 | 0.350ms | 248.730ms | 0.020ms |
  | fifo   |   01 | 0.357ms | 248.817ms | 0.024ms |
  | other  |  -20 | 0.399ms | 249.906ms | 0.020ms |
  | other  |   19 | 0.477ms | 297.756ms | 0.022ms |

The key metrics above are the average and max latencies (wall time).
These improvements should roughly translate to p95-p99 latencies on real
workloads. The response time is up to 200x faster in these scenarios and
there is no penalty in the regular path.

Note that it is only possible to convert this lock after a series of
changes made by previous patches. These mainly include refactoring the
sections that might_sleep() and changing the locking order with the
mmap_lock amongst others.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20231201172212.1813387-29-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-12-05 09:23:41 +09:00

183 lines
6.3 KiB
C

/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (C) 2017 Google, Inc.
*/
#ifndef _LINUX_BINDER_ALLOC_H
#define _LINUX_BINDER_ALLOC_H
#include <linux/rbtree.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/list_lru.h>
#include <uapi/linux/android/binder.h>
extern struct list_lru binder_freelist;
struct binder_transaction;
/**
* struct binder_buffer - buffer used for binder transactions
* @entry: entry alloc->buffers
* @rb_node: node for allocated_buffers/free_buffers rb trees
* @free: %true if buffer is free
* @clear_on_free: %true if buffer must be zeroed after use
* @allow_user_free: %true if user is allowed to free buffer
* @async_transaction: %true if buffer is in use for an async txn
* @oneway_spam_suspect: %true if total async allocate size just exceed
* spamming detect threshold
* @debug_id: unique ID for debugging
* @transaction: pointer to associated struct binder_transaction
* @target_node: struct binder_node associated with this buffer
* @data_size: size of @transaction data
* @offsets_size: size of array of offsets
* @extra_buffers_size: size of space for other objects (like sg lists)
* @user_data: user pointer to base of buffer space
* @pid: pid to attribute the buffer to (caller)
*
* Bookkeeping structure for binder transaction buffers
*/
struct binder_buffer {
struct list_head entry; /* free and allocated entries by address */
struct rb_node rb_node; /* free entry by size or allocated entry */
/* by address */
unsigned free:1;
unsigned clear_on_free:1;
unsigned allow_user_free:1;
unsigned async_transaction:1;
unsigned oneway_spam_suspect:1;
unsigned debug_id:27;
struct binder_transaction *transaction;
struct binder_node *target_node;
size_t data_size;
size_t offsets_size;
size_t extra_buffers_size;
unsigned long user_data;
int pid;
};
/**
* struct binder_lru_page - page object used for binder shrinker
* @page_ptr: pointer to physical page in mmap'd space
* @lru: entry in binder_freelist
* @alloc: binder_alloc for a proc
*/
struct binder_lru_page {
struct list_head lru;
struct page *page_ptr;
struct binder_alloc *alloc;
};
/**
* struct binder_alloc - per-binder proc state for binder allocator
* @lock: protects binder_alloc fields
* @vma: vm_area_struct passed to mmap_handler
* (invariant after mmap)
* @mm: copy of task->mm (invariant after open)
* @buffer: base of per-proc address space mapped via mmap
* @buffers: list of all buffers for this proc
* @free_buffers: rb tree of buffers available for allocation
* sorted by size
* @allocated_buffers: rb tree of allocated buffers sorted by address
* @free_async_space: VA space available for async buffers. This is
* initialized at mmap time to 1/2 the full VA space
* @pages: array of binder_lru_page
* @buffer_size: size of address space specified via mmap
* @pid: pid for associated binder_proc (invariant after init)
* @pages_high: high watermark of offset in @pages
* @oneway_spam_detected: %true if oneway spam detection fired, clear that
* flag once the async buffer has returned to a healthy state
*
* Bookkeeping structure for per-proc address space management for binder
* buffers. It is normally initialized during binder_init() and binder_mmap()
* calls. The address space is used for both user-visible buffers and for
* struct binder_buffer objects used to track the user buffers
*/
struct binder_alloc {
spinlock_t lock;
struct vm_area_struct *vma;
struct mm_struct *mm;
unsigned long buffer;
struct list_head buffers;
struct rb_root free_buffers;
struct rb_root allocated_buffers;
size_t free_async_space;
struct binder_lru_page *pages;
size_t buffer_size;
int pid;
size_t pages_high;
bool oneway_spam_detected;
};
#ifdef CONFIG_ANDROID_BINDER_IPC_SELFTEST
void binder_selftest_alloc(struct binder_alloc *alloc);
#else
static inline void binder_selftest_alloc(struct binder_alloc *alloc) {}
#endif
enum lru_status binder_alloc_free_page(struct list_head *item,
struct list_lru_one *lru,
spinlock_t *lock, void *cb_arg);
struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc,
size_t data_size,
size_t offsets_size,
size_t extra_buffers_size,
int is_async);
void binder_alloc_init(struct binder_alloc *alloc);
int binder_alloc_shrinker_init(void);
void binder_alloc_shrinker_exit(void);
void binder_alloc_vma_close(struct binder_alloc *alloc);
struct binder_buffer *
binder_alloc_prepare_to_free(struct binder_alloc *alloc,
unsigned long user_ptr);
void binder_alloc_free_buf(struct binder_alloc *alloc,
struct binder_buffer *buffer);
int binder_alloc_mmap_handler(struct binder_alloc *alloc,
struct vm_area_struct *vma);
void binder_alloc_deferred_release(struct binder_alloc *alloc);
int binder_alloc_get_allocated_count(struct binder_alloc *alloc);
void binder_alloc_print_allocated(struct seq_file *m,
struct binder_alloc *alloc);
void binder_alloc_print_pages(struct seq_file *m,
struct binder_alloc *alloc);
/**
* binder_alloc_get_free_async_space() - get free space available for async
* @alloc: binder_alloc for this proc
*
* Return: the bytes remaining in the address-space for async transactions
*/
static inline size_t
binder_alloc_get_free_async_space(struct binder_alloc *alloc)
{
size_t free_async_space;
spin_lock(&alloc->lock);
free_async_space = alloc->free_async_space;
spin_unlock(&alloc->lock);
return free_async_space;
}
unsigned long
binder_alloc_copy_user_to_buffer(struct binder_alloc *alloc,
struct binder_buffer *buffer,
binder_size_t buffer_offset,
const void __user *from,
size_t bytes);
int binder_alloc_copy_to_buffer(struct binder_alloc *alloc,
struct binder_buffer *buffer,
binder_size_t buffer_offset,
void *src,
size_t bytes);
int binder_alloc_copy_from_buffer(struct binder_alloc *alloc,
void *dest,
struct binder_buffer *buffer,
binder_size_t buffer_offset,
size_t bytes);
#endif /* _LINUX_BINDER_ALLOC_H */