B737 Captain reported the descent profile for the CAVLR6 STAR to IAD is too steep for the B737 right after the PERKN intersection and noted that most of the time the flight crew receives a steep descent message on the FMC on this arrival.

Narrative

I have seen this same situation numerous times on the 737; but not all the time. On the CAVLR6 STAR; there is a crossing restriction to cross PERKN at or above FL220. About 75% of the time on this arrival; we receive a 'steep descent after PERKN' message on the FMC; but this time we did not. Autopilot was ON; FO was flying pilot; LNAV and VNAV engaged; ATC gave a 'descend via the CAVLR6; landing south.' 4000 feet was set in the altitude window. We began the VNAV descent out of FL250; and when we got close to PERKN; although the autopilot was ON; and LNAV and VNAV were engaged; the autopilot did not abide by the altitude restriction of FL220 or above at PERKN. We were about two miles from PERKN descending through FL220; and since it happened so quick; it was quicker for me as the pilot monitoring (PM); to click off the autopilot and level the airplane to try and abide by the altitude restriction at PERKN. Before I could stop the airplane from descending; we had descended to approximately 21;700 about 1.5 miles prior to PERKN. I then handed the airplane back to the FO; and he continued to slowly climb us back to FL220. As always on this STAR; the profile is way too steep for the airplane directly after PERKN; so the VNAV PATH dropped into VNAV SPD; and we were high on the descent path. The FO reengaged the autopilot and used speed brakes to try and descend to get us on the VNAV PATH. We continued the descend via clearance; but barely made the altitude and speed restriction at CAVLR because the airplane had a steep descent after PERKN. The rest of the arrival was uneventful; and we continued to a landing.I normally see this situation when we have a very strong tailwind; but today we had a quartering headwind of approximately 25 kt.The descent profile for this STAR is way too steep for the 737 right after the PERKN intersection. For some reason; even though there is a big altitude restriction window at KHOOD; the software program of this airplane wants to start an extremely steep descent after PERKN; sometimes up to 4;000 - 6;000 FPM rate of descent.