  Recent studies of the optical/UV and X-ray ephemerides of X1822-371 have
found some discrepancies in the value of the orbital period derivative. Because
of the importance of this value in constraining the system evolution, we
comprehensively analyse all the available optical/UV/X eclipse times of this
source to investigate the origin of these discrepancies. We collected all
previously published X-ray eclipse times from 1977 to 2008, to which we added
the eclipse time observed by Suzaku in 2006. This point is very important to
cover the time gap between the last RXTE eclipse time (taken in 2003) and the
most recent Chandra eclipse time (taken in 2008). Similarly we collected the
optical/UV eclipse arrival times covering the period from 1979 to 2006, adding
a further eclipse time taken on 1978 and updating previous optical/UV
ephemeris. We compared the X-ray and the optical/UV ephemeris, and finally
derived a new ephemeris of the source by combining the eclipse arrival times in
the X-ray and optical/UV bands. The X-ray eclipse time delays calculated with
respect to a constant orbital period model display a clear parabolic trend,
confirming that the orbital period of this source constantly increases at a
rate of $\dot{P}_{\rm{orb}} =1.51(7) \times 10^{-10}$ s/s. Combining the X-ray
and the optical/UV data sets, we find that $\dot{P}_{\rm{orb}} =1.59(9) \times
10^{-10}$ s/s, which is compatible with the X-ray orbital solution. We also
investigate the possible presence of a delay of the optical/UV eclipse with
respect to the X-ray eclipse, finding that this delay may not be constant in
time. In particular, this variation is compatible with a sinusoidal modulation
of the optical/UV eclipse arrival times with respect to the long-term parabolic
trend. In this case, the optical/UV eclipse should lag the X-ray eclipse and
the time-lag oscillate about an average value. (Abridged)
