Hi,

I am using curl-loader to simulate 5000 users generating HTTP/s traffic to a nginx server, find that curl-loader consumes many time on c-ares initiation. Please look the attached gprof output.

Via checking the libcurl source code, the function Curl_resolver_init() do the c-ares initiation, and curl_easy_init() calls this function via Curl_open(). So we need to do the c-ares initiation every time when we want to initialize a curl handler.
Via checking the C-ares souce code, there are two large 'for' loops in function ares_init_options(),
                #define ARES_QID_TABLE_SIZE 2048
#define ARES_TIMEOUT_TABLE_SIZE 1024
  for (i = 0; i < ARES_QID_TABLE_SIZE; i++)
    {
      ares__init_list_head(&(channel->queries_by_qid[i]));
    }
  for (i = 0; i < ARES_TIMEOUT_TABLE_SIZE; i++)
    {
      ares__init_list_head(&(channel->queries_by_timeout[i]));
    }
So, even when we only send a single GET request, curl will call ares__init_list_head() thousands times. That's the reason why curl-loader consumes so many time on c-ares initiation.

My question is if we can do the c-ares initiation only once but not in every curl_easy_init()? By that probably we can increase the curl-loader performance significantly.

Some gprof output:
Flat profile:

Each sample counts as 0.01 seconds.
  % cumulative self self total
time seconds seconds calls ms/call ms/call name
18.46 0.12 0.12 9186352 0.00 0.00 ares__init_list_head
12.31 0.20 0.08 1 80.00 80.00 build_url_set
10.77 0.27 0.07 81473 0.00 0.00 dprintf_formatf
  9.23 0.33 0.06 3325 0.02 0.07 ares_init_options
  4.62 0.36 0.03 1770 0.02 0.04 create_conn
  3.08 0.38 0.02 107452 0.00 0.00 client_tracing_function
  3.08 0.40 0.02 41568 0.00 0.00 fd_key_compare
  3.08 0.42 0.02 5102 0.00 0.01 epoll_dispatch
  3.08 0.44 0.02 3150 0.01 0.01 ares_library_initialized
  3.08 0.46 0.02 2243 0.01 0.01 ares_cancel
  1.54 0.47 0.01 6918787 0.00 0.00 ares__is_list_empty
  1.54 0.48 0.01 450212 0.00 0.00 alloc_addbyter
  1.54 0.49 0.01 227162 0.00 0.00 aresx_uztosi
  1.54 0.50 0.01 107005 0.00 0.00 hostcache_timestamp_remove
  1.54 0.51 0.01 56835 0.00 0.00 Curl_pgrsUpdate
  1.54 0.52 0.01 33870 0.00 0.00 Curl_splay
  1.54 0.53 0.01 16682 0.00 0.00 event_add
  1.54 0.54 0.01 14075 0.00 0.00 Curl_readwrite
  1.54 0.55 0.01 12624 0.00 0.00 event_active
  1.54 0.56 0.01 10776 0.00 0.00 ares__get_hostent
  1.54 0.57 0.01 8906 0.00 0.00 ares_expand_name
  1.54 0.58 0.01 3484 0.00 0.01 init_by_resolv_conf
  1.54 0.59 0.01 2062 0.00 0.00 Curl_he2ai
  1.54 0.60 0.01 1663 0.01 0.02 Curl_http
  1.54 0.61 0.01 823 0.01 0.01 next_load_cb_hyper
  1.54 0.62 0.01 727 0.01 0.03 Curl_hash_clean_with_criterium
  1.54 0.63 0.01 616 0.02 0.02 curl_multi_perform
  1.54 0.64 0.01 Curl_resolver_cleanup

Thanks,
Simon
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