The small dots are most probably hard silicate material, stuck very securely to the glass.
Loose dirt needs to be removed first, then oily films.
1. Rinse the windscreen with water.
2. Scrub the windscreen thoroughly with an old pot scourer, using a strong mixture of car shampoo and water.
3. Scrape the windscreen with NEW razor blade installed in a paint scarper.
4. Clean with a commercial glass cleaner.
In most cases, oily films on the inside of the glass can be removed a commercial glass cleaner and large paper towel.