X-Git-Url: http://git.joshuawise.com/netwatch.git/blobdiff_plain/c00c1c15f28f3d926d9ce500417265f8afe72eca..3c4e084de9ed00171748c20de1251d347fc33c1c:/README diff --git a/README b/README index 2977c05..a673c33 100644 --- a/README +++ b/README @@ -6,12 +6,19 @@ taking over a second network card to provide a standard VNC server, such that a machine elsewhere on the network can see the text or graphics console of the machine and inject keystrokes as needed. - . - - . - - Because NetWatch is invisible to the OS, its CPU usage is difficult to -monitor; we do so by comparing the MD5 throughput of the system with NetWatch + System management mode, introduced with the 386SL, essentially allows +system driver code to run outside of OS control, caused by a special interrupt +pin on the CPU. This was originally intended for applications such as laptop +fan control; it is also the mechansim by which USB legacy keyboard emulation +occurs. When a system management interrupt occurs, the northbridge remaps +portions of memory to expose previously-hidden code, and asserts an SMI# signal, +causing the CPU to save all its state into system management RAM and vector to +a magic entry point. + + This is somewhat slow, and so there is a moderate performance impact +caused by running NetWatch, more significant when a VNC session is open. +Because NetWatch is invisible to the OS, its CPU usage is difficult to monitor; +we do so by comparing the MD5 throughput of the system with NetWatch running versus without. The only way that the OS could detect this performance drain is by spinning tightly and watching for a sudden jump in the CPU's time stamp counters. @@ -49,4 +56,5 @@ implementation requires: - BIOS which does not set the D_LCK bit. Any system old enough to be based on the ICH2 is very likely to have a suitable BIOS. - Current open issues are listed in the TODO file. + Current open issues are listed in the TODO file. See GUIDE for an +overview of which source files do what.