Quoting r. Libor Michalek <[EMAIL PROTECTED]>: > Subject: Re: SDP: BUG 2034 workaround > > On Tue, Feb 22, 2005 at 12:14:45PM +0200, Michael S. Tsirkin wrote: > > > > sdp_inet.c, inside _sdp_inet_listen, we have: > > > > #if 0 /* BUG 2034 workaround. */ > > conn->backlog_max = backlog; > > #else > > conn->backlog_max = 1024; > > #endif > > > > What gives? what would be the proper fix as opposed to a work-around? > > The Linux TCP listen uses two seperate values to control the listner > backlog, so I ignored the backlog parameter to get closer to the default > Linux behavior, until a really solution is devised. > > Basically TCP uses a two stage backlog to defend against SYN attacks. > When a SYN is received a small amount of state is kept until the full > handshake is completed, at which point a full socket is created and > queued onto the listen sockets accept queue. The second stage uses the > listen() backlog parameter to manage the accept queue. The first stage > queue size is managed using a sysctl, (net.pv4.tcp_max_syn_backlog) > which on a lot of systems defaults to 1024. > > SDP on the other hand creates the full socket on the REQ request, and > places it directly into the listen sockets accept queue. So the full > depth of the queue is governed by the listen backlog parameter. Worse > still the socket layer listen, above TCP and SDP, limits the listen() > backlog that is passed to the protocol to 128, and only recently did this > become adjustable using net.core.somaxconn. > > Using just the backlog parameter to manage this queue, results in a > few programs that use a high connection volume to get rejected connection, > casued by a full backlog queue, even when upped to the full 128 that the > socket layer allows by default. > > > -Libor >
I see. A protocol bug. I wander if some application could get confused if it gets more connections it set the backlog up for. What do you think? For now, a somewhat cleaner work-around would be: 1. Replace the /* BUG 2034 workaround. */ comment with the excellent explanation above. 2. Take the max value between the socket backlog and sysctl_max_syn_backlog. Want a patch like that? -- MST - Michael S. Tsirkin _______________________________________________ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
