I wouldn't do it now as the flower buds will be forming. Wait until all flowering has finished. Then cut back all the long tendrils, possibly cut it back by a third. I'm not an expert on Wisteria but someone here will tell you if I'm right.

I was at a talk a few weeks ago where the speaker said wisteria can be pruned in any month beginning with J. So June or July for long whippy growths, and January for major reduction.