Since you upgraded me to Yosemite,
I make your Mac go slow;
But when, you cannot possibly know.
You think that your modem speed is back to 56K,
as you wait for each web page, to display.
Speedtest.net says that your net connection is, in fact, OK.
As I’m indexing the things I’ve found,
I speed up your mac, and then slow it down.
Simply to frustrate, and make you frown.
Who am I?
Hint: Answer to this riddle can be found in the previous posting.