Wiadomość napisana przez Robert Watson w dniu 7 maj 2014, o godz. 13:49: > On Wed, 7 May 2014, Edward Tomasz Napierala wrote: > >> Author: trasz >> Date: Wed May 7 06:38:19 2014 >> New Revision: 265498 >> URL: http://svnweb.freebsd.org/changeset/base/265498 >> >> Log: >> MFC r264025: >> >> Get rid of the "autoscaling", instead just set socket buffer sizes >> in the usual way. The only thing the old code did was making things >> less predictable. > > Does this mean that the autoscaling algorithm needs refining? The problem > with disabling autoscaling is that the code may, in the future, fail to > benefit from further global refinements, as old code that hard-coded sizes > now fails to do -- and that if we don't refine the autoscaling model, other > applications may fail to benefit.
The commit message here was misleading - what got replaced was setting the socket buffer size "by hand" to a value computed from negotiated maximum PDU size. Now it's set to constant size. The reason we do not use autoscaling here is not performance. It's because iSCSI code can't transmit a part of PDU; it always waits until there is room for the whole thing (PDUs can be up to about 128kB in size). If the socket buffer size somehow got autoscaled below that amount, the transmit would stop indefinitely. There is a somewhat similar situation on the receive side. So, the right solution would be to either use autoscaling, but with a guarantee that the socket buffer won't shrink below some specified value, or have a way to determine that the socket buffer won't get any bigger anytime soon and so the iSCSI should transmit or receive a part of PDU. Current setting "by hand" is just a workaround, albeit pretty well working one. _______________________________________________ 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"
