OK, I guess I typed right into that one didn't I :)
I'm surprised the wording is as strong as it is. Tpchashsz is something we've been tuning on most of our SPECweb9X submittals with HP-UX 11 for years and years now.
I guess some of it stems from ifyou make tcphashsz too big your kernel might not boot :)
Basically, tcphashsz controls the sizes of a number of internal TCP hash tables.
If the cut and paste works, what follows is a descrpition. I thought it was online at
www.spec.org someplace as part of a SPECweb submittal but could not find it.
There are seven dynamically allocated hash lists in TCP and IP. The sizes
of these lists are controlled by the HP/UX configuration variable
tcphashsz. Since this single variable controls the size of multiple
lists, it is treated as a relative scale factor, rather than as the
actual size of any specific list. The relative sizes of the individual
lists are fixed. The absolute sizes are determined by the product of
the scale factor and the relative size.
The seven hash lists are:
ipc_tcp_fanout IP's list of all established TCP connections.
ipc_tcp_listeners IP's list of all TCP listeners.
ipc_udp_fanout IP's list of all bound UDP streams.
tcp_port_hash_arr All TCP's by local port.
tcp_listener_hash_arr All TCP listeners by port.
tcp_establshd_hash_arr All established TCP connections.
tcp_lock_list TCP's distributed lock list.
When allocating the above hash lists, the value of the HP/UX configuration
variable tcphashsz is first rounded down to the next lowest power of two.
It is then bounded on the low side at 64 and on the high side at 64K.
If tcphashsz is specified as zero, a default value of 2048 is used.
If we use 'A' to indicate the value of the resulting scale factor, the
following table lists the actual sizes of the allocation, in words, for
each of the seven lists:
ipc_tcp_fanout A / 2
ipc_tcp_listeners A / 4
ipc_udp_fanout A / 4
tcp_port_hash_arr A
tcp_listener_hash_arr A / 4
tcp_establshd_hash_arr A / 2
tcp_lock_list A / 16
The following table gives actual list sizes, in words, and total space
allocated, in bytes, for several example values of tcphashsz:
64 256 2048 16K 32K 64K
-----------------------------------------------------------------------
ipc_tcp_fanout 32 128 1024 8192 16K 32K
ipc_tcp_listeners 16 64 512 4096 8K 16K
ipc_udp_fanout 16 64 512 4096 8K 16K
tcp_port_hash_arr 64 256 2048 16K 32K 64K
tcp_listener_hash_arr 16 64 512 4096 8K 16K
tcp_establshd_hash_arr 32 128 1024 8192 16K 32K
tcp_lock_list 4 16 128 1024 2K 4K
-----------------------------------------------------------------------
total space (in bytes) 720 2880 23040 184320 368640 737280
I've no idea if it will format well, so I'll try to have a copy at
ftp://ftp.cup.hp.com/dist/networking/briefs/tcphashsz.txt
there is no rest for the wicked yet the virtuous have no pillows
