Performance impact can be mitigated if patches applied correctly
Newer versions of the KPTI (formally KAISER) patches in Linux will allow applying the address space separation only on certain processes. The separation is useful to performance, because most code stacks managing SAN and NAS machines divide execution between non critical and critical core processes, so theoretically you can apply the KPTI only to the non-critical parts which can run non-critical user facing things such as nodejs, ssh, and various other third-parties, and leave the performance-critical proprietary data path in its set of processes with KPTI disabled, and thus with performance unhampered.