Commit 809850b7 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman

tty: Use lockless flip buffer free list

In preparation for lockless flip buffers, make the flip buffer
free list lockless.

NB: using llist is not the optimal solution, as the driver and
buffer work may contend over the llist head unnecessarily. However,
test measurements indicate this contention is low.
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2cf7b67e
......@@ -44,16 +44,17 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size)
void tty_buffer_free_all(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *p;
struct tty_buffer *p, *next;
struct llist_node *llist;
while ((p = buf->head) != NULL) {
buf->head = p->next;
kfree(p);
}
while ((p = buf->free) != NULL) {
buf->free = p->next;
llist = llist_del_all(&buf->free);
llist_for_each_entry_safe(p, next, llist, free)
kfree(p);
}
buf->tail = NULL;
buf->memory_used = 0;
}
......@@ -68,22 +69,20 @@ void tty_buffer_free_all(struct tty_port *port)
* allocation behaviour.
* Return NULL if out of memory or the allocation would exceed the
* per device queue
*
* Locking: Caller must hold tty->buf.lock
*/
static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
{
struct tty_buffer **tbh = &port->buf.free;
struct llist_node *free;
struct tty_buffer *p;
/* Round the buffer size out */
size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
if (size <= MIN_TTYB_SIZE) {
if (*tbh) {
p = *tbh;
*tbh = p->next;
free = llist_del_first(&port->buf.free);
if (free) {
p = llist_entry(free, struct tty_buffer, free);
goto found;
}
}
......@@ -109,8 +108,6 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
*
* Free a tty buffer, or add it to the free list according to our
* internal strategy
*
* Locking: Caller must hold tty->buf.lock
*/
static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
......@@ -123,10 +120,8 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
if (b->size > MIN_TTYB_SIZE)
kfree(b);
else {
b->next = buf->free;
buf->free = b;
}
else
llist_add(&b->free, &buf->free);
}
/**
......@@ -542,7 +537,7 @@ void tty_buffer_init(struct tty_port *port)
spin_lock_init(&buf->lock);
buf->head = NULL;
buf->tail = NULL;
buf->free = NULL;
init_llist_head(&buf->free);
buf->memory_used = 0;
INIT_WORK(&buf->work, flush_to_ldisc);
}
......
......@@ -124,6 +124,29 @@ static inline void init_llist_head(struct llist_head *list)
&(pos)->member != NULL; \
(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
/**
* llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
* safe against removal of list entry
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @node: the first entry of deleted list entries.
* @member: the name of the llist_node with the struct.
*
* In general, some entries of the lock-less list can be traversed
* safely only after being removed from list, so start with an entry
* instead of list head.
*
* If being used on entries deleted from lock-less list directly, the
* traverse order is from the newest to the oldest added entry. If
* you want to traverse from the oldest to the newest, you must
* reverse the order by yourself before traversing.
*/
#define llist_for_each_entry_safe(pos, n, node, member) \
for (pos = llist_entry((node), typeof(*pos), member); \
&pos->member != NULL && \
(n = llist_entry(pos->member.next, typeof(*n), member), true); \
pos = n)
/**
* llist_empty - tests whether a lock-less list is empty
* @head: the list to test
......
......@@ -11,6 +11,7 @@
#include <linux/tty_flags.h>
#include <uapi/linux/tty.h>
#include <linux/rwsem.h>
#include <linux/llist.h>
......@@ -30,7 +31,10 @@
#define __DISABLED_CHAR '\0'
struct tty_buffer {
struct tty_buffer *next;
union {
struct tty_buffer *next;
struct llist_node free;
};
int used;
int size;
int commit;
......@@ -65,7 +69,7 @@ struct tty_bufhead {
spinlock_t lock;
struct tty_buffer *head; /* Queue head */
struct tty_buffer *tail; /* Active buffer */
struct tty_buffer *free; /* Free queue head */
struct llist_head free; /* Free queue head */
int memory_used; /* Buffer space used excluding
free queue */
};
......
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