Author: gallatin Date: Wed Sep 11 18:48:26 2019 New Revision: 352228 URL: https://svnweb.freebsd.org/changeset/base/352228
Log: Avoid unneeded call to arc4random() in syncache_add() Don't call arc4random() unconditionally to initialize sc_iss, and then when syncookies are enabled, just overwrite it with the return value from from syncookie_generate(). Instead, only call arc4random() to initialize sc_iss when syncookies are not enabled. Note that on a system under a syn flood attack, arc4random() becomes quite expensive, and the chacha_poly crypto that it calls is one of the more expensive things happening on the system. Removing this unneeded arc4random() call reduces CPU from about 40% to about 35% in my test scenario (Broadwell Xeon, 6Mpps syn flood attack). Reviewed by: rrs, tuxen, bz Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D21591 Modified: head/sys/netinet/tcp_syncache.c Modified: head/sys/netinet/tcp_syncache.c ============================================================================== --- head/sys/netinet/tcp_syncache.c Wed Sep 11 18:40:05 2019 (r352227) +++ head/sys/netinet/tcp_syncache.c Wed Sep 11 18:48:26 2019 (r352228) @@ -1543,7 +1543,6 @@ skip_alloc: sc->sc_todctx = todctx; #endif sc->sc_irs = th->th_seq; - sc->sc_iss = arc4random(); sc->sc_flags = 0; sc->sc_flowlabel = 0; @@ -1617,6 +1616,8 @@ skip_alloc: if (V_tcp_syncookies) sc->sc_iss = syncookie_generate(sch, sc); + else + sc->sc_iss = arc4random(); #ifdef INET6 if (autoflowlabel) { if (V_tcp_syncookies) _______________________________________________ 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"
