Single-channel hypothesis - Oxford Reference
AS Level PE - Single channel hypothesis, anticipation and psychological refractory …
Division of attention: The single-channel hypothesis …
We have seen increasing cases of antivirus leading to significant performance problems. Companies are more likely to run quite intrusive antivirus even on critical, production machines. The antivirus settings are usually corporate-wide and may be inappropriate or insufficiently tuned for particular applications or workloads. In some cases, even when an antivirus administrator states that antivirus has been "disabled," there may still be kernel level modules that are still operational. In some cases, slowdowns are truly difficult to understand; for example, in one case a slowdown occurred because of a network issue communicating with the antivirus hub, but this occurred at a kernel-level driver in fully native code, so it was very difficult even to hypothesize that it was antivirus. You can use operating system level tools and sampling profilers to check for such cases, but they may not always be obvious. Keep a watch out for signs of antivirus and consider running a benchmark comparison with and without antivirus (completely disabled, perhaps even uninstalled).
"The IBM® JIT compiler is tuned for long-running applications typically used on a server. You can use the -Xquickstart command-line option to improve the performance of short-running applications, especially for applications in which processing is not concentrated into a few methods.
-Xquickstart causes the JIT compiler to use a lower optimization level by default and to compile fewer methods. Performing fewer compilations more quickly can improve application startup time. When the AOT compiler is active (both shared classes and AOT compilation enabled), -Xquickstart causes all methods selected for compilation to be AOT compiled, which improves the startup time of subsequent runs. -Xquickstart might degrade performance if it is used with long-running applications that contain methods using a large amount of processing resource. The implementation of -Xquickstart is subject to change in future releases." ()
A Level PE Friday, 31 October 2008
In general, if two hosts are communicating on a LAN and there is sufficient additional network capacity and there is sufficient additional CPU interrupt processing capacity, then disabling delayed acknowledgments will tend to improve performance and throughput. However, this option is normally set at an operating system level, so if there are any sockets on the box that may go out to a WAN, then their performance and throughput may potentially be affected negatively. Even on a WAN, for 95% of modern internet connections, disabling delayed acknowledgments may prove beneficial. The most important thing to do is to test the change with real world traffic, and also include tests emulating users with very slow internet connections and very far distances to the customer data center (e.g. second long ping times) to understand any impact. The other potential impact of disabling delayed acknowledgments is that there will be more packets which just have the acknowledgment bit set but still have the TCP/IP header (40 or more bytes). This may cause higher network utilization and network CPU interrupts (and thus CPU usage). These two factors should be monitored before and after the change.
Try to present the 2nd stimuli as close to the first as possible for maximum effect. Psychological Refractory Period (PRP)The PRP works alongside the single channel hypothesis.
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