Ask HN: How do you ensure the scalability and performance of your product?

If you're working on a SaaS or PaaS - how does your company ensure that the product scales with the business and its performance is kept at an acceptable level? I'm especially interested in the team layout to support this - is this a shared responsibility for all development teams or are there specialized teams? How do you spread the knowledge/skills around this topic among the engineers? Is the product organization focusing on this? How do you manage to allocate time for this, how do you priotitize such workstreams agains e.g. features?