On 31.07.2013 4:15, David O'Brien wrote: > On Tue, Jul 30, 2013 at 05:07:46PM -0700, David O'Brien (@FreeBSD) wrote: >> I believe you're talking about this code in >> sys/libkern/arc4random.c:arc4rand() >> >> if (atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE, >> ARC4_ENTR_SEED) || reseed || >> (arc4_numruns > ARC4_RESEED_BYTES) || >> (tv.tv_sec > arc4_t_reseed)) >> arc4_randomstir(); > > Looking at this, seems to me that it would be more optimized if we tested > the things that are most likely to be TRUE first instead of those things > most likely to be FALSE? ARC4_ENTR_HAVE->ARC4_ENTR_SEED can only happen > once per boot, and the 'reseed' flag is '0' in the majority of the > arc4rand() callers. >
This code can be called concurrently, so the first part is to reseed immediately if we have good entropy, making other threads wait for the lock released in arc4_randomstir() and arc4_t_reseed, arc4_numruns reset, so they don't call arc4_randomstir() in chain, if possible (small window still exists, as it was in original code). While there is no harm for arc4 algo itself to call arc4_randomstir() several times in line, it is just CPU waste. I don't touch the order of the rest conditions. -- http://ache.vniz.net/ bitcoin:1G6ugdNY6e5jx1GVnAU2ntj2NEfmjKG85r _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
