Well, while a good intention I don't think providing a setopt for that is a very good idea. Users won't know what to set it to. I think we can start with doing an #ifdef-thing for different environments' conditions and we can start with only special-casing win32...

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** [bugs:#1228] curl multi timeout does not work with timeout set less than 40ms**
**Status:** open
**Created:** Wed May 22, 2013 09:45 PM UTC by Hang
**Last Updated:** Mon Jun 03, 2013 10:28 PM UTC
**Owner:** Daniel Stenberg
In the latest source code lib/multi.c:
~~~~
2178   now.tv_usec += 40000; /* compensate for bad precision timers that might've
2179                            triggered too early */
2180   if(now.tv_usec >= 1000000) {
2181     now.tv_sec++;
2182     now.tv_usec -= 1000000;
2183   }
2184 
2185   /*
2186    * The loop following here will go on as long as there are expire-times left
2187    * to process in the splay and 'data' will be re-assigned for every expired
2188    * handle we deal with.
2189    */
2190   do {
2191     /* the first loop lap 'data' can be NULL */
2192     if(data) {
2193       do
2194         result = multi_runsingle(multi, now, data->set.one_easy);
2195       while(CURLM_CALL_MULTI_PERFORM == result);
~~~~
"now" has been artificially incremented by 40ms, and then passed in to the multi_runsingle(...) below. 
Then, multi_runsingle() will check for timeouts:
~~~~
964       timeout_ms = Curl_timeleft(data, &now,
965                                  (easy->state <= CURLM_STATE_WAITDO)?
966                                  TRUE:FALSE);
~~~~
so, if the timeout setting is less than 40ms for the curl easy handle, the Curl_tvdiff(*nowp, data->progress.t_startsingle) will return 39ms at the very beginning of the curl easy request, and therefore timeout the request even before it gets started. 
It will always prompt something like this (almost immediately after the first curl_multi_perform() call):
http://foo.com => (28) Connection timed out after 39 milliseconds
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