linux-kernel - Re: [PATCH v3 2/2] TTY: tty flip buffer optimisation.

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Date:	Mon, 14 Nov 2011 15:25:47 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Ilya Zykov <ilya@...x.ru>
CC:	Alan Cox <alan@...ux.intel.com>, linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: [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@...h:~/src/pty$ time ./bench_pty_buf 253
> chunk = 253. loop = 3952569.
> real	0m21.017s
> user	0m0.436s
> sys	0m17.749s
> 
> ilya@...h:~/src/pty$ time ./bench_pty_buf 255
> chunk = 255. loop = 3921568.
> real	0m21.276s
> user	0m0.544s
> sys	0m17.329s
> 
> ilya@...h:~/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@...x.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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