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SubjectRe: [PATCH v3 2/2] TTY: tty flip buffer optimisation.
On 11/14/2011 01:47 PM, Ilya Zykov wrote:
> Currently, free flip buffer (tty->buf.free) reserve memory for further used,
> only if driver send to ldisc less 257 bytes in one time.
> If driver send more, flip buffer reserve(kmalloc()) and then
> free(kfree()) every chunk more 256 bytes every time.
>
>
> This patch allow reserve more than 256 bytes chunks in free buffer.
> And have self-regulation chunk size ability(very useful for pty).
> Also we can control memory used(at the most TTY_BUFFER_MAX).
> And avoiding useless looking up buffer more then 256 byte size.
>
> With this patch I get follow results:
>
> ilya@serh:~/src/pty$ time ./bench_pty_buf 253
> chunk = 253. loop = 3952569.
> real 0m21.017s
> user 0m0.436s
> sys 0m17.749s
>
> ilya@serh:~/src/pty$ time ./bench_pty_buf 255
> chunk = 255. loop = 3921568.
> real 0m21.276s
> user 0m0.544s
> sys 0m17.329s
>
> ilya@serh:~/src/pty$ time ./bench_pty_buf 257
> chunk = 257. loop = 3891050.
> real 0m21.652s
> user 0m0.512s
> sys 0m18.593s

Hi, the results are indeed nice. However is there any *real* load other
than this tailor-made microbenchmark where the added code complexity is
worth it?

BTW am I guessing correctly that PATCH 1/2 should contain *no* patch in
fact? That it's just to present the benchmark sources?

> Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
> ---
> diff -uprN -X ../../dontdiff a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> --- a/drivers/tty/tty_buffer.c 2011-11-12 00:19:27.000000000 +0400
> +++ b/drivers/tty/tty_buffer.c 2011-11-14 15:55:45.000000000 +0400
> @@ -58,8 +58,21 @@ static struct tty_buffer *tty_buffer_all
> {
> struct tty_buffer *p;
> - if (tty->buf.memory_used + size > 65536)
> - return NULL;
> + if (tty->buf.memory_reserve + size > TTY_BUFFER_MAX) {
> + /* If possible, free small chunks
> + have been had total size = "size". */
> + if (tty->buf.memory_reserve - tty->buf.memory_used >= size)
> + while (tty->buf.memory_reserve + size >
> + TTY_BUFFER_MAX) {
> + p = tty->buf.free;
> + tty->buf.free = p->next;
> + tty->buf.memory_reserve -= p->size;
> + WARN_ON(tty->buf.memory_reserve < 0);
> + kfree(p);
> + }
> + else
> + return NULL;
> + }
> p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
> if (p == NULL)
> return NULL;
> @@ -71,6 +84,7 @@ static struct tty_buffer *tty_buffer_all
> p->char_buf_ptr = (char *)(p->data);
> p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
> tty->buf.memory_used += size;
> + tty->buf.memory_reserve += size;
> return p;
> }
> @@ -91,11 +105,12 @@ static void tty_buffer_free(struct tty_s
> tty->buf.memory_used -= b->size;
> WARN_ON(tty->buf.memory_used < 0);
> - if (b->size >= 512)
> - kfree(b);
> - else {
> + if (tty->buf.free != NULL) {
> b->next = tty->buf.free;
> tty->buf.free = b;
> + } else {
> + tty->buf.free = b;
> + b->next = NULL;
> }
> }
> @@ -517,6 +532,7 @@ void tty_buffer_init(struct tty_struct *
> tty->buf.tail = NULL;
> tty->buf.free = NULL;
> tty->buf.memory_used = 0;
> + tty->buf.memory_reserve = 0;
> INIT_WORK(&tty->buf.work, flush_to_ldisc);
> }
> diff -uprN -X ../../dontdiff a/include/linux/tty.h b/include/linux/tty.h
> --- a/include/linux/tty.h 2011-11-12 00:19:27.000000000 +0400
> +++ b/include/linux/tty.h 2011-11-14 14:51:21.000000000 +0400
> @@ -82,7 +82,7 @@ struct tty_buffer {
> */
> #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
> -
> +#define TTY_BUFFER_MAX 65536
> struct tty_bufhead {
> struct work_struct work;
> @@ -90,6 +90,7 @@ struct tty_bufhead {
> struct tty_buffer *head; /* Queue head */
> struct tty_buffer *tail; /* Active buffer */
> struct tty_buffer *free; /* Free queue head */
> + int memory_reserve; /* Buffer space used */
> int memory_used; /* Buffer space used excluding
> free queue */
> };

thanks,
--
js
suse labs


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