Author: sobomax
Date: Thu Nov 29 19:28:01 2018
New Revision: 341257
URL: https://svnweb.freebsd.org/changeset/base/341257
Log:
Replace hand-crafted naive byte-by-byte zero block detection routine
with macro based around memcmp(). The latter is expected to be some
8 times faster on a modern 64-bit architectures.
In practice, throughput of doing conv=sparse from /dev/zero to /dev/null
went up some 5-fold here from 1.9GB/sec to 9.7GB/sec with this change
(bs=128k).
MFC after: 2 weeks
Modified:
head/bin/dd/dd.c
head/bin/dd/dd.h
Modified: head/bin/dd/dd.c
==============================================================================
--- head/bin/dd/dd.c Thu Nov 29 19:13:10 2018 (r341256)
+++ head/bin/dd/dd.c Thu Nov 29 19:28:01 2018 (r341257)
@@ -511,7 +511,7 @@ void
dd_out(int force)
{
u_char *outp;
- size_t cnt, i, n;
+ size_t cnt, n;
ssize_t nw;
static int warned;
int sparse;
@@ -544,12 +544,8 @@ dd_out(int force)
do {
sparse = 0;
if (ddflags & C_SPARSE) {
- sparse = 1; /* Is buffer sparse? */
- for (i = 0; i < cnt; i++)
- if (outp[i] != 0) {
- sparse = 0;
- break;
- }
+ /* Is buffer sparse? */
+ sparse = BISZERO(outp, cnt);
}
if (sparse && !force) {
pending += cnt;
Modified: head/bin/dd/dd.h
==============================================================================
--- head/bin/dd/dd.h Thu Nov 29 19:13:10 2018 (r341256)
+++ head/bin/dd/dd.h Thu Nov 29 19:28:01 2018 (r341257)
@@ -103,3 +103,7 @@ typedef struct {
#define C_PROGRESS 0x40000000
#define C_PARITY (C_PAREVEN | C_PARODD | C_PARNONE | C_PARSET)
+
+#define BISZERO(p, s) ((s) > 0 && *((const char *)p) == 0 && !memcmp(
\
+ (const void *)(p), (const void *) \
+ ((const char *)p + 1), (s) - 1))
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