AIX Version 4.3 Differences Guide

performance of network memory buffers (mbufs), filesystem I/O, raw I/O, and
page I/O.
In previous AIX versions, during a DMA operation, the majority of pathlength was
spent in page translation/lookup paths to get the virtual to physical address
translations for DMA.
The term pretranslation refers to the concept of performing the virtual to physical
address translations for a data buffer to be involved in a DMA operation once, for
the life of the data buffer, instead of for each individual I/O setup for the buffer. In
general, a subsystem desiring to benefit from the performance gain of
pretranslation calls a new kernel service passing in a buffer address, length, and
cross-memory descriptor. The kernel service will attach to the cross memory
descriptor pretranslation information for the buffer. Then, whenever the buffer is
used for I/O, the DMA services recognize the presence of pretranslation info in
the cross-memory descriptor and avoid page table lookups.
There is no change required by device drivers to take advantage of this
enhancement, as long as a network driver is using mbufs from the global
net_malloc pool and performing dynamic on-the-fly DMA mappings (compared
with copying data to premapped buffers).
4.9 Fast fork() Function (4.3.1)
AIX Version 4.3.1 introduces a fast-fork function called f_fork() that is based on
IEEE POSIX specifications. The f_fork() call is precisely like fork() except:
• It is required that the child process calls one of the exec functions immediately
after it is created. Since fork handlers are never called, the application data,
mutexes, and the locks are all undefined in the child process.
The use of f_fork() will significantly enhances the performance of Internet and
Web server applications that need to create many short lived child processes.
4.10 New Sockets System Call (4.3.2)
AIX 4.3.2 has added the new send_file() system call. Its use is aimed at
applications that transmit file data across the network using a socket connection.
It offers a speed improvement over the traditional method of sending a file across
the network by avoiding unnecessary data copying where possible.
#include
ssize_t send_file(Socket_p, sf_iobuf, flags)
int *Socket_p;
struct sf_parms *sf_iobuf;
uint_t flags;
Using send_file eliminates the need to read a file just to send it across the
network. Applications can remove the read() call, and therefore avoid redundant
transfer of data between kernel space and user space. The send_file call reads
file data into the new Network Buffer Cache (NBC). The NBC is allocated from an
area of the mbuf pool and uses mbufs for file data storage. The networking
subsystem then transmits the data directly from the mbufs in the NBC across the
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