Subject: Re: [PATCH] fetch-pack: add tracing for negotiation rounds

From: Josh Steadmon <[email-masked]>
Date: Tue, 2 Aug 2022 14:52:15 -0700

On 2022.07.25 20:04, Jeff Hostetler wrote:
> 
> 
> On 7/25/22 6:13 PM, Josh Steadmon wrote:
> > Currently, negotiation for V0/V1/V2 fetch have trace2 regions covering
> > the entire negotiation process. However, we'd like additional data, such
> > as timing for each round of negotiation or the number of "haves" in each
> > round. Additionally, "independent negotiation" (AKA push negotiation)
> > has no tracing at all. Having this data would allow us to compare the
> > performance of the various negotation implementations, and to debug
> > unexpectedly slow fetch & push sessions.
> > 
> > Fix this by adding per-round trace2 regions for all negotiation
> > implementations (V0+V1, V2, and independent negotiation), as well as an
> > overall region for independent negotiation. Add trace2 data logging for
> > the number of haves and "in vain" objects for each round, and for the
> > total number of rounds once negotiation completes.  Finally, add a few
> > checks into various tests to verify that the number of rounds is logged
> > as expected.
> 
> I've been wanting to add data like this around the negotiation
> code for a while now.  Thanks!
> 
> > 
> > Signed-off-by: Josh Steadmon <[email-masked]>
> > ---
> >   fetch-pack.c                       | 62 +++++++++++++++++++++++++++++-
> >   t/t5500-fetch-pack.sh              |  4 +-
> >   t/t5516-fetch-push.sh              | 10 ++++-
> >   t/t5601-clone.sh                   |  6 ++-
> >   t/t5703-upload-pack-ref-in-want.sh |  6 ++-
> >   5 files changed, 81 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fetch-pack.c b/fetch-pack.c
> > index cb6647d657..01a451e456 100644
> > --- a/fetch-pack.c
> > +++ b/fetch-pack.c
> > @@ -299,6 +299,7 @@ static int find_common(struct fetch_negotiator *negotiator,
> >   {
> >   	int fetching;
> >   	int count = 0, flushes = 0, flush_at = INITIAL_FLUSH, retval;
> > +	int negotiation_round = 0, haves = 0;
> >   	const struct object_id *oid;
> >   	unsigned in_vain = 0;
> >   	int got_continue = 0;
> > @@ -441,9 +442,19 @@ static int find_common(struct fetch_negotiator *negotiator,
> >   		packet_buf_write(&req_buf, "have %s\n", oid_to_hex(oid));
> >   		print_verbose(args, "have %s", oid_to_hex(oid));
> >   		in_vain++;
> > +		haves++;
> >   		if (flush_at <= ++count) {
> >   			int ack;
> > +			negotiation_round++;
> > +			trace2_region_enter_printf("negotiation_v0_v1", "round",
> > +						   the_repository, "round-%d",
> > +						   negotiation_round);
> 
> I'm wondering here if the "round-%d" should have some number
> of leading zeros so that multiple rounds will sort correctly
> when you have a bunch of them.
> 
> I'm also wondering (and this is more of a style thing, so feel
> free to ignore) if we could just use trace2_region_enter()
> and make the "label" field be the "round/%04d" and not need
> the extra args.

Junio suggested just dropping the prefix altogether, so that's what I've
done for V2, but if you feel strongly about it we can discuss further
for V3.

> > +			trace2_data_intmax("negotiation_v0_v1", the_repository,
> > +					   "haves_added", haves);
> > +			trace2_data_intmax("negotiation_v0_v1", the_repository,
> > +					   "in_vain", in_vain);
> > +			haves = 0;
> 
> Thanks,
> Jeff