The wild swings in market volatility has been a blessing for many hedge funds this year. But for others, it's been a curse.

The Cboe Volatility index, the fear tracker known as the Vix, has more than halved in the six weeks since it hit an all-time high on 16 March. Long-volatility funds have reaped big rewards — the Cboe Eurekahedge Long Volatility Hedge Fund Index returned about 40% in the first three months of 2020.