On 04/29/12 20:53, Matthew Wallace wrote: Hoping this is the right forum for this question - I've noticed a peculiar limit when setting net.inet.udp.recvspace using sysctl. This value cannot be any larger than 5591040 bytes - any value larger than that gives the error message "Result too large". This is on a MacPro running OS X 10.7.3. Can anybody give me any clue as to where this limitation comes from and if there's any way around it? A while back (10.6?) Apple made socket buffer sizes conditional on the amount of number of mbuf clusters. The value you're trying to adjust is limited by sb_max. That, in turn, is set by kern.ipc.maxsockbuf. That is limited to 1/16 of the amount of memory allocated to network buffers. I think the goal was to prevent one or two connections from being able to starve the entire machine. The easiest fix is to increase the number of mbuf clusters using the ncl=??? argument. The default mbuf cluster pool size is 64MB (32768 2KB clusters), and the maxsockbuf limit is indeed 1/16 of that: root@macpro03:~# sysctl -a | egrep nmbcl\|maxsockb kern.ipc.maxsockbuf: 4194304 kern.ipc.nmbclusters: 32768 To fix this, tell the system to use more than the default 32768 mbufclusters via the ncl boot arg: root@macpro02:~# nvram boot-args="ncl=131072" root@macpro02:~# shutdown -r now When the machine comes back up, it has more mbuf clusters, and will allow you to raise kern.ipc.maxsockbuf: root@macpro02:~# sysctl -w kern.ipc.maxsockbuf=16777216 kern.ipc.maxsockbuf: 8388608 -> 16777216 root@macpro02:~# sysctl -a | egrep nmbcl\|maxsockb kern.ipc.maxsockbuf: 16777216 kern.ipc.nmbclusters: 131072 Now you can finally increase udp recvspace: root@macpro02:~# sysctl -w net.inet.udp.recvspace=8388608 net.inet.udp.recvspace: 42080 -> 8388608 Drew _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.... This email sent to site_archiver@lists.apple.com