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); _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
