On 2022.07.25 16:07, Junio C Hamano wrote:
> Josh Steadmon <steadmon@xxxxxxxxxx> writes:
>
> > 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.
>
> Quite sensibly argued. I do not necessarily see the current code as
> "broken", and "fix" at the beginning of the next line may not be an
> appropriate word to describe this enhancement, but I think it would
> be nice to have such numbers.
Reworded that sentence.
> > 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);
>
> Not an objection, but all the hits to existing calls to this
> function show the data in a format as vanilla as possible without
> frills (presumably to make it easier to mechanically parse the value
> out when needed???), and the "round-" prefix we see here somehow
> looks out of place. Doesn't the fact that the record is in the
> "negotiation_v0_v1" category and has label "round" clear enough sign
> that the value presented is the negotiation_round?
True, fixed in V2.
> > + 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;
> > packet_buf_flush(&req_buf);
> > send_request(args, fd[1], &req_buf);
> > strbuf_setlen(&req_buf, state_len);
> > @@ -465,6 +476,9 @@ static int find_common(struct fetch_negotiator *negotiator,
> > ack, oid_to_hex(result_oid));
> > switch (ack) {
> > case ACK:
> > + trace2_region_leave_printf("negotiation_v0_v1", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
> > flushes = 0;
> > multi_ack = 0;
> > retval = 0;
> > @@ -490,6 +504,7 @@ static int find_common(struct fetch_negotiator *negotiator,
> > const char *hex = oid_to_hex(result_oid);
> > packet_buf_write(&req_buf, "have %s\n", hex);
> > state_len = req_buf.len;
> > + haves++;
> > /*
> > * Reset in_vain because an ack
> > * for this commit has not been
> > @@ -510,14 +525,26 @@ static int find_common(struct fetch_negotiator *negotiator,
> > flushes--;
> > if (got_continue && MAX_IN_VAIN < in_vain) {
> > print_verbose(args, _("giving up"));
> > + trace2_region_leave_printf("negotiation_v0_v1", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
> > break; /* give up */
> > }
> > - if (got_ready)
> > + if (got_ready) {
> > + trace2_region_leave_printf("negotiation_v0_v1", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
> > break;
> > + }
> > + trace2_region_leave_printf("negotiation_v0_v1", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
> > }
>
> Having many duplicated calls to "leave" makes the whole thing look
> somewhat confused. Is this primarily because we have too many
> "break" that breaks out of the loop?
Yes, although now that I look at it again, I believe as soon as we
finish the do-while, we know that the round is over, so I believe we can
just put a single region_leave there. Fixed in V2.
> > @@ -1603,6 +1632,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
> > struct oidset common = OIDSET_INIT;
> > struct packet_reader reader;
> > int in_vain = 0, negotiation_started = 0;
> > + int negotiation_round = 0;
> > int haves_to_send = INITIAL_FLUSH;
> > struct fetch_negotiator negotiator_alloc;
> > struct fetch_negotiator *negotiator;
> > @@ -1659,6 +1689,10 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
> > "negotiation_v2",
> > the_repository);
> > }
> > + negotiation_round++;
> > + trace2_region_enter_printf("negotiation_v2", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
> > if (send_fetch_request(negotiator, fd[1], args, ref,
> > &common,
> > &haves_to_send, &in_vain,
> > @@ -1686,12 +1720,20 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
> > } else {
> > do_check_stateless_delimiter(args->stateless_rpc, &reader);
> > state = FETCH_SEND_REQUEST;
> > + trace2_region_leave_printf("negotiation_v2", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
> > }
> > break;
> > case FETCH_GET_PACK:
> > + trace2_region_leave_printf("negotiation_v2", "round",
> > + the_repository, "round-%d",
> > + negotiation_round);
>
> Hmph. Doesn't this logically belong to the "FETCH_PROCESS_ACKS"
> case arm? We "leave" the current round when we did not get "ready"
> and "enter" the next round by moving to "FETCH_SEND_REQUEST" state,
> but at the same location when we did get "ready", we can "leave" the
> current (and final) round and move to "FETCH_GET_PACK" state. I
> suspect the code structure and control flow becomes easier to see
> when expressed that way.
That works, but then we also need an additional region_leave in the
FETCH_SEND_REQUEST case where we jump directly to FETCH_GET_PACK. I'm
not sure which way is more intuitive, but I've gone with your suggestion
for V2.
> > trace2_region_leave("fetch-pack",
> > "negotiation_v2",
> > the_repository);
> > + trace2_data_intmax("negotiation_v2", the_repository,
> > + "total_rounds", negotiation_round);
> > /* Check for shallow-info section */
> > if (process_section_header(&reader, "shallow-info", 1))
> > receive_shallow_info(args, &reader, shallows, si);
