JPMorgan analyst Sterling Auty recommends using today's selloff in shares of FireEye as a buying opportunity. The analyst says the metric he cares about the most, billings, generated double-digit growth in Q2, ahead of his expectation. However, the "noise" caused by the company's revenue outlook cut and the impact on earnings will likely be what investors focus on, Auty tells investors in a post-earnings research note. Billings growth is the leading indicator of where revenue will go, but the time to conversion is now pushed out in terms of double digit revenue growth, he adds. At current share levels, though, Auty thinks investors are "being rewarded to wait for the revenue growth and bookings growth to converge." He keeps an Overweight rating on FireEye with a $20 price target.