HEADS UP: UNIX domain socket locking changes merged to CVS HEAD

Dear all,

After on-and-off development since 2005, I've now merged the UNIX domain 
socket locking patch.  Special thanks to Kris Kennaway who has been providing 
stability testing, performance testing, and general support and feedback for 
this project since inception.

Please let me know if you experience any problems with UNIX domain sockets -- 
these changes will affect applications that consume UNIX domain sockets 
directly, like MySQL and Postfix, as well as consumers of POSIX fifos, which 
are implemented using UNIX domain sockets in-kernel.

Thanks,

Robert N M Watson
Computer Laboratory
University of Cambridge

---------- Forwarded message ----------
Date: Mon, 26 Feb 2007 20:47:52 +0000 (UTC)
From: Robert Watson <rwatson_at_FreeBSD.org>
To: src-committers_at_FreeBSD.org, cvs-src_at_FreeBSD.org, cvs-all_at_FreeBSD.org
Subject: cvs commit: src/sys/sys unpcb.h src/sys/kern uipc_usrreq.c

rwatson     2007-02-26 20:47:52 UTC

   FreeBSD src repository

   Modified files:
     sys/sys              unpcb.h
     sys/kern             uipc_usrreq.c
   Log:
   Revise locking strategy used for UNIX domain sockets in order to improve
   concurrency:

   - Add per-unpcb mutexes protecting unpcb connection state, fields, etc.

   - Replace global UNP mutex with a global UNP rwlock, which will protect the
     UNIX domain socket connection topology, v_socket, and be acquired
     exclusively before acquiring more than per-unpcb at a time in order to
     avoid lock order issues.

   In performance measurements involving MySQL, this change has little or no
   overhead on UP (+/- 1%), but leads to a significant (5%-30%) improvement in
   multi-processor measurements using the sysbench and supersmack benchmarks.

   Much testing by:        kris
   Approved by:            re (kensmith)

   Revision  Changes    Path
   1.197     +468 -222  src/sys/kern/uipc_usrreq.c
   1.22      +1 -0      src/sys/sys/unpcb.h