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From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sun, 12 May 2019 06:32:46 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r347500 - head/sys/libkern
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Author: mjg
Date: Sun May 12 06:32:46 2019
New Revision: 347500
URL: https://svnweb.freebsd.org/changeset/base/347500
Log:
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
Modified:
head/sys/libkern/arc4random.c
Modified: head/sys/libkern/arc4random.c
==============================================================================
--- head/sys/libkern/arc4random.c Sat May 11 22:58:25 2019 (r347499)
+++ head/sys/libkern/arc4random.c Sun May 12 06:32:46 2019 (r347500)
@@ -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);