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tty: Enable configurable tty flip buffer limit

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Allow driver to configure its maximum flip buffer memory
consumption/limit. This is necessary for very-high speed line
rates (in excess of 10MB/sec) because the flip buffers can
be saturated before the line discipline has a chance to
throttle the input.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-11-22 12:09:55 -05:00 • committed by Greg Kroah-Hartman
parent 82f91fe092
commit 4d18e6eff8
3 changed files with 23 additions and 3 deletions
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24
drivers/tty/tty_buffer.c
View file

@ -26,7 +26,7 @@
* Byte threshold to limit memory consumption for flip buffers. * Byte threshold to limit memory consumption for flip buffers.
* The actual memory limit is > 2x this amount. * The actual memory limit is > 2x this amount.
*/ */
#define TTYB_MEM_LIMIT 65536 #define TTYB_DEFAULT_MEM_LIMIT 65536
/* /*
* We default to dicing tty buffer allocations to this many characters * We default to dicing tty buffer allocations to this many characters
@ -89,7 +89,7 @@ void tty_buffer_unlock_exclusive(struct tty_port *port)
int tty_buffer_space_avail(struct tty_port *port) int tty_buffer_space_avail(struct tty_port *port)
{ {
int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used); int space = port->buf.mem_limit - atomic_read(&port->buf.memory_used);
return max(space, 0); return max(space, 0);
} }
@ -162,7 +162,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
/* Should possibly check if this fails for the largest buffer we /* Should possibly check if this fails for the largest buffer we
have queued and recycle that ? */ have queued and recycle that ? */
if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT) if (atomic_read(&port->buf.memory_used) > port->buf.mem_limit)
return NULL; return NULL;
p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC); p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
if (p == NULL) if (p == NULL)
@ -536,4 +536,22 @@ void tty_buffer_init(struct tty_port *port)
atomic_set(&buf->memory_used, 0); atomic_set(&buf->memory_used, 0);
atomic_set(&buf->priority, 0); atomic_set(&buf->priority, 0);
INIT_WORK(&buf->work, flush_to_ldisc); INIT_WORK(&buf->work, flush_to_ldisc);
buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
} }
/**
* tty_buffer_set_limit - change the tty buffer memory limit
* @port: tty port to change
*
* Change the tty buffer memory limit.
* Must be called before the other tty buffer functions are used.
*/
int tty_buffer_set_limit(struct tty_port *port, int limit)
{
if (limit < MIN_TTYB_SIZE)
return -EINVAL;
port->buf.mem_limit = limit;
return 0;
}
EXPORT_SYMBOL_GPL(tty_buffer_set_limit);

1
include/linux/tty.h
View file

@ -61,6 +61,7 @@ struct tty_bufhead {
struct tty_buffer sentinel; struct tty_buffer sentinel;
struct llist_head free; /* Free queue head */ struct llist_head free; /* Free queue head */
atomic_t memory_used; /* In-use buffers excluding free list */ atomic_t memory_used; /* In-use buffers excluding free list */
int mem_limit;
struct tty_buffer *tail; /* Active buffer */ struct tty_buffer *tail; /* Active buffer */
}; };
/* /*

1
include/linux/tty_flip.h
View file

@ -1,6 +1,7 @@
#ifndef _LINUX_TTY_FLIP_H #ifndef _LINUX_TTY_FLIP_H
#define _LINUX_TTY_FLIP_H #define _LINUX_TTY_FLIP_H
extern int tty_buffer_set_limit(struct tty_port *port, int limit);
extern int tty_buffer_space_avail(struct tty_port *port); extern int tty_buffer_space_avail(struct tty_port *port);
extern int tty_buffer_request_room(struct tty_port *port, size_t size); extern int tty_buffer_request_room(struct tty_port *port, size_t size);
extern int tty_insert_flip_string_flags(struct tty_port *port, extern int tty_insert_flip_string_flags(struct tty_port *port,