def before_train_epoch(self, runner) -> None:
        """fix lr of predictor by epoch."""
        if self.fix_pred_lr:
            for param_group in runner.optim_wrapper.optimizer.param_groups:
                if 'fix_lr' in param_group and param_group['fix_lr']:
                    param_group['lr'] = self.lr
fix lr of predictor by epoch.
mmpretrain/engine/hooks/simsiam_hook.py