Curl/php: execution time?

Using CURL/PHP, how can I measure server's execution time? and what is the diference b/w STARTTRANSFER_TIME and 开发者_如何转开发PRETRANSFER_TIME ?

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Regarding STARTTRANSFER_TIME and PRETRANSFER_TIME.

Starttransfer_time

Pass a pointer to a double to receive the time, in seconds, it took from the start until the first byte is just about to be transferred. This includes CURLINFO_PRETRANSFER_TIME and also the time the server needs to calculate the result

Pretransfer_time

Pass a pointer to a double to receive the time, in seconds, it took from the start until the file transfer is just about to begin. This includes all pre-transfer commands and negotiations that are specific to the particular protocol(s) involved