Re: [flashrom] [PATCH] Reduce realloc syscall overhead for ft2232 and bitbang

[Paul Fox]

carl-daniel wrote:
> Reduce realloc syscall overhead for FT2232 and bitbang.
>
> FT2232 ran realloc() for every executed command. Start with a big enough
> buffer and don't touch buffer size unless it needs to grow.
> Bitbang was slightly better: It only ran realloc() if buffer size
> changed. Still, the solution above improves performance and reliability.

this is fine, but i'm curious -- did you measure a performance
change, or is this "by inspection"?  it's never been my
impression that historically realloc would be slow, unless the
buffer is growing -- in which case there's no choice.  and my perhaps
mistaken assumption was that realloc() would usually not shrink a
buffer.

paul
> Signed-off-by: Carl-Daniel Hailfinger
> Index: flashrom-realloc_overhead/bitbang_spi.c
>
> --- flashrom-realloc_overhead/bitbang_spi.c	(Revision 777)
> +++ flashrom-realloc_overhead/bitbang_spi.c	(Arbeitskopie)
> @@ -87,14 +87,16 @@
>    static unsigned char *bufout = NULL;
>    static unsigned char *bufin = NULL;
>    static int oldbufsize = 0;
> int bufsize = max(writecnt + readcnt, 260);
>
> int bufsize;
> int i;
>
> /* Arbitrary size limitation here. We're only constrained by memory. */
> if (writecnt > 65536 || readcnt > 65536)
> return SPI_INVALID_LENGTH;
> if (bufsize != oldbufsize) {
> bufsize = max(writecnt + readcnt, 260);
> /* Never shrink. realloc() calls are expensive. */
> if (bufsize > oldbufsize) {
> bufout = realloc(bufout, bufsize);
> if (!bufout) {
> 	fprintf(stderr, "Out of memory!\n");
>
> @@ -109,6 +111,7 @@
>    			free(bufout);
>    		exit(1);
>    	}
> oldbufsize = bufsize;
> }
>
> memcpy(bufout, writearr, writecnt);
> Index: flashrom-realloc_overhead/ft2232_spi.c
>
> --- flashrom-realloc_overhead/ft2232_spi.c	(Revision 777)
> +++ flashrom-realloc_overhead/ft2232_spi.c	(Arbeitskopie)
> @@ -200,14 +200,22 @@
>    static unsigned char *buf = NULL;
>    /* failed is special. We use bitwise ops, but it is essentially bool. */
>    int i = 0, ret = 0, failed = 0;
>
> int bufsize;
>
> static int oldbufsize = 0;
>
> if (writecnt > 65536 || readcnt > 65536)
> return SPI_INVALID_LENGTH;
> buf = realloc(buf, writecnt + readcnt + 100);
> if (!buf) {
> fprintf(stderr, "Out of memory!\n");
> exit(1); // -1
>
> /* buf is not used for the response from the chip. */
>
> bufsize = max(writecnt + 9, 260);
>
> /* Never shrink. realloc() calls are expensive. */
>
> if (bufsize > oldbufsize) {
> buf = realloc(buf, bufsize);
> if (!buf) {
> 	fprintf(stderr, "Out of memory!\n");
> 	exit(1);
> }
> oldbufsize = bufsize;
>
> }
>
> /*

=---------------------
 paul fox, [e-mail] (arlington, ma, where it's 47.1 degrees)