Right and they have a LOT of GPUs from Nvidia for handle the unknown. Custom silicon for custom workloads seems like a good strategy specially considering the capabilities that the team will develop along the way.
Offloading a known workload to a custom chip can also save a lot on operations costs, particularly power. Facebook is interested in workload operations per watt rather than raw floating point operations per watt. A GPU might have better raw specs but if the whole GPU package has worse workload ops per watt, a custom chip is likely better.
At Facebook's scale the spherical cow raw performance stats don't matter nearly as much as real world workloads per ops dollar. They can also repurpose their GPUs to other workloads and let their custom chips handle the boring baseline stuff.
At Facebook's scale the spherical cow raw performance stats don't matter nearly as much as real world workloads per ops dollar. They can also repurpose their GPUs to other workloads and let their custom chips handle the boring baseline stuff.