bitwise_rscan() is found to be hot spot in ovn-controller during OVN
scalability tests. It is triggered by lflow_run() when processing
lflow updates from SB ovsdb. The perf result shows:
+ 34.21% ovn-controller ovn-controller [.] bitwise_rscan
+ 16.08% ovn-controller libc-2.15.so [.] 0x80810
+ 7.39% ovn-controller [kernel.kallsyms] [k] 0xffffffff8103e0ba
+ 5.74% ovn-controller ovn-controller [.] lex_token_parse
+ 4.31% ovn-controller ovn-controller [.] ovsdb_idl_next_row
+ 2.84% ovn-controller ovn-controller [.] lflow_run
After optimization, bitwise_rscan percentage dropped from 34% to less
than 5%:
+ 23.69% ovn-controller libc-2.15.so [.] 0x13a586
+ 13.47% ovn-controller [kernel.kallsyms] [k] 0xffffffff8103e0ba
+ 5.44% ovn-controller ovn-controller [.] ovsdb_idl_next_row
+ 5.03% ovn-controller ovn-controller [.] lex_token_parse
+ 4.81% ovn-controller ovn-controller [.] bitwise_rscan
+ 3.62% ovn-controller ovn-controller [.] lflow_run
Signed-off-by: Han Zhou <zhou...@gmail.com>
---
lib/util.c | 33 ++++++++++++++++++++++++++++-----
1 file changed, 28 insertions(+), 5 deletions(-)
diff --git a/lib/util.c b/lib/util.c
index f06dee5..b0887fb 100644
--- a/lib/util.c
+++ b/lib/util.c
@@ -1400,14 +1400,37 @@ bitwise_scan(const void *p, unsigned int len, bool
target, unsigned int start,
int
bitwise_rscan(const void *p, unsigned int len, bool target, int start, int end)
{
- int ofs;
+ const uint8_t *s = p;
+ int start_byte = len - (start / 8 + 1);
+ int end_byte = len - (end / 8 + 1);
+ int ofs_byte;
+ int try;
+ for (try = 0; try < 2; try++) {
+ for (ofs_byte = start_byte; ofs_byte <= end_byte; ofs_byte++) {
+ if ((target && s[ofs_byte])
+ || (!target && (s[ofs_byte] != 0xff))) {
+ break;
+ }
+ }
+ if (ofs_byte > end_byte) {
+ return end;
+ }
- for (ofs = start; ofs > end; ofs--) {
- if (bitwise_get_bit(p, len, ofs) == target) {
- break;
+ uint8_t the_byte = s[ofs_byte];
+ int ofs;
+ for (ofs = 7; ofs >= 0; ofs--) {
+ if (((the_byte & (1u << ofs)) != 0) == target) {
+ break;
+ }
+ }
+ int ret = (len - ofs_byte) * 8 - (8 - ofs);
+ if (ret < end) {
+ return end;
+ } else if (ret <= start) {
+ return ret;
}
}
- return ofs;
+ return -1; /* Should never reach here */
}
/* Copies the 'n_bits' low-order bits of 'value' into the 'n_bits' bits
--
2.1.0
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