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

[Carl-Daniel Hailfinger]

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.

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;
    }

/*