MultiStepParamScheduler: allow num_updates to be at the end of milest…

…ones

Summary: This is easier to config: just use [30, 60, 90, 120] instead of two separate configs

Reviewed By: theschnitz

Differential Revision: D27108999

fbshipit-source-id: f8ad25c62656c429d30ea29b7fa4dcbe960540a5

detectron2/solver/build.py

@@ -246,7 +246,7 @@ def build_lr_scheduler(
     sched = WarmupParamScheduler(
         sched,
         cfg.SOLVER.WARMUP_FACTOR,
-        cfg.SOLVER.WARMUP_ITERS / cfg.SOLVER.MAX_ITER,
+        min(cfg.SOLVER.WARMUP_ITERS / cfg.SOLVER.MAX_ITER, 1.0),
         cfg.SOLVER.WARMUP_METHOD,
     )
     return LRMultiplier(optimizer, multiplier=sched, max_iter=cfg.SOLVER.MAX_ITER)