I've moved an existing asp.net web-api over from an Azure VM (with IIS and MSSQL installed locally) to an Azure web app and Azure SQL database (both west-europe). I'm noticing a dramatic increase in processing duration between the two for the same workload. Tasks that take 10-15ms on the VM, take at least 150ms in the hosted service environment. Both internal processing, not including network latency to/from the vm or web app. Both with empty databases and the same code-base. Same database schema with the same indexing.
The VM was a simple 2-core/7GB SSD machine. But even when I set my web app to a premium 4-core/7GB and my database to a premium 250DTU, the performance does not increase at all. In fact, its the same on a basic 2-core web app and 10DTU database. So the bottleneck has to be somewhere else.
How would I go about finding out what causes the slow processing? The web app and database show no performance alerts and don't advise scaling up either.