Conrad Meyer 179f62805c random(4): Fortuna: allow increased concurrency ... Add experimental feature to increase concurrency in Fortuna. As this diverges slightly from canonical Fortuna, and due to the security sensitivity of random(4), it is off by default. To enable it, set the tunable kern.random.fortuna.concurrent_read="1". The rest of this commit message describes the behavior when enabled. Readers continue to update shared Fortuna state under global mutex, as they do in the status quo implementation of the algorithm, but shift the actual PRF generation out from under the global lock. This massively reduces the CPU time readers spend holding the global lock, allowing for increased concurrency on SMP systems and less bullying of the harvestq kthread. It is somewhat of a deviation from FS&K. I think the primary difference is that the specific sequence of AES keys will differ if READ_RANDOM_UIO is accessed concurrently (as the 2nd thread to take the mutex will no longer receive a key derived from rekeying the first thread). However, I believe the goals of rekeying AES are maintained: trivially, we continue to rekey every 1MB for the statistical property; and each consumer gets a forward-secret, independent AES key for their PRF. Since Chacha doesn't need to rekey for sequences of any length, this change makes no difference to the sequence of Chacha keys and PRF generated when Chacha is used in place of AES. On a GENERIC 4-thread VM (so, INVARIANTS/WITNESS, numbers not necessarily representative), 3x concurrent AES performance jumped from ~55 MiB/s per thread to ~197 MB/s per thread. Concurrent Chacha20 at 3 threads went from roughly ~113 MB/s per thread to ~430 MB/s per thread. Prior to this change, the system was extremely unresponsive with 3-4 concurrent random readers; each thread had high variance in latency and throughput, depending on who got lucky and won the lock. "rand_harvestq" thread CPU use was high (double digits), seemingly due to spinning on the global lock. After the change, concurrent random readers and the system in general are much more responsive, and rand_harvestq CPU use dropped to basically zero. Tests are added to the devrandom suite to ensure the uint128_add64 primitive utilized by unlocked read functions to specification. Reviewed by: markm Approved by: secteam(delphij) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D20313		2019-06-17 20:29:13 +00:00
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Makefile
uint128_test.c	random(4): Fortuna: allow increased concurrency	2019-06-17 20:29:13 +00:00