AIX Version 4.3 Differences Guide

2.6.2 Debug Modifications
Since the debugger cannot store to some areas in virtual mode due to kernel
protection, the debugger has been altered so that all stores to virtual memory
addresses are first transplanted and then performed in real mode. This operation
is transparent to the debug user. It requires a modification to the
get_put_data_aligned() routine so that virtual operations are translated and
performed in real mode. I/O space has not been affected.
2.6.3 Stack Overflow Protection
A stack overflow detection mechanism has been implemented. i_poll() and
i_poll_soft() check the MST save-area located lower in memory to see if the
csa_prev values, that would be used if the interrupt is interrupted, are valid. If this
location contains incorrect data, it is repaired if possible, and the code logs an
error.
2.7 SMP TTY Handling
Currently on J30 and J40 SMP systems equipped with 128-port adapters, when
the system is under load, CPU 0 spends a great deal of time off-level polling the
various 128-port adapters for incoming events.
To alleviate this problem, instead of CPU 0 being used as a timer handler, the
load has been passed to other CPUs that are available, thereby improving the
overall SMP performance.
2.8 Faster Per-Thread Data
In previous versions of AIX, all threads shared an identical address space. When
per-thread data needed to be accessed, a fairly expensive lookup had to be
performed by the get_thread_specific() routine.
In a non-threaded version of the OpenGL API (which is very call intensive), tests
show that you can expect to spend roughly 150 cycles per call (on average) in a
routine. Using the existing get-thread-specific() routine would add approximately
70 cycles (or 50 percent overhead) to enable a multi-threaded OpenGL API. A
much faster mechanism to access per-thread data for 32-bit systems is therefore
required. For 32-bit systems, a separate segment 0 for each processor is now
provided. This segment contains a page of thread-specific data that is modified
as each thread is swapped in. Faster access to private memory should also
provide benefits to the thread libraries.
2.9 Expanded Limits on Open Files (4.3.1)
In previous versions of AIX, a single process was limited to a maximum of 2000
open files at any one time. There was also a total system-wide limit of 200,000
open files. This number was entirely arbitrary, and although it was perfectly
adequate for most processes, it was not enough for some. AIX Version 4.3.1
increases these limits to the following.
• Maximum of 1,048,576 open files system wide.
• Maximum of 32,767 open files per process.
AIX Kernel Enhancements 19