On Wed, Mar 16, 2016 at 10:03 PM, Ben Pfaff <b...@ovn.org> wrote:
> 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?
>
The first try doesn't check if the first found bit is in "start_byte" but
before the "start" bit. In such case, the second try will do the real job
to find the correct bit.
I will add some documentation.
--
Best regards,
Han
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