On Wed, Mar 16, 2016 at 08:55:35PM -0700, Han Zhou wrote:
> 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++) {
Why does the code need two tries?
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