From 95034c44e6ba9e5e2532353b5cac1ad714817f47 Mon Sep 17 00:00:00 2001 From: mjg Date: Sun, 12 May 2019 06:32:46 +0000 Subject: [PATCH] random(4): depessimize arc4random - __predict_false reseeding on entry as it is almost never true. - don't blindly atomic_cmpset as on x86 it ends up dirtying the cacheline. it almost ever succeeds per above - fetch the timestamp prior to getting the cpu number Reviewed by: cem Approved by: secteam (delphij) Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D20242 --- sys/libkern/arc4random.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/sys/libkern/arc4random.c b/sys/libkern/arc4random.c index 313ec986c80..4f733e5cef8 100644 --- a/sys/libkern/arc4random.c +++ b/sys/libkern/arc4random.c @@ -173,18 +173,20 @@ arc4rand(void *ptr, u_int len, int reseed) u_int length; u_int8_t *p; - if (reseed || atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE, ARC4_ENTR_SEED)) + if (__predict_false(reseed || + (arc4rand_iniseed_state == ARC4_ENTR_HAVE && + atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE, ARC4_ENTR_SEED)))) CHACHA20_FOREACH(chacha20) chacha20_randomstir(chacha20); - chacha20 = &chacha20inst[curcpu]; getmicrouptime(&tv); + chacha20 = &chacha20inst[curcpu]; /* We may get unlucky and be migrated off this CPU, but that is expected to be infrequent */ if ((chacha20->numbytes > CHACHA20_RESEED_BYTES) || (tv.tv_sec > chacha20->t_reseed)) chacha20_randomstir(chacha20); - mtx_lock(&chacha20->mtx); p = ptr; + mtx_lock(&chacha20->mtx); while (len) { length = MIN(CHACHA20_BUFFER_SIZE, len); chacha_encrypt_bytes(&chacha20->ctx, chacha20->m_buffer, p, length); -- 2.45.0