Hello, I'm interesting in timing OS overhead for disk accesses. As I've discussed with Avadh in private emails, I've extended the MARSS_DELAY_IO code in qemu/hw/ide/core.c to support an SSD simulation. At this point, I want to understand how much OS overhead is introduced for the operations to my disk simulation.
I'd like to do the following: * Have a C++ program that does a small file read (and make sure the file is not cached in RAM ahead of time). * Do rdtsc before and after the read (times A and D). * On the hardware side, whenever I receive the disk IO command to my mods in ptlsim.cpp, I'd like to grab the time stamp counter at the beginning and end of the access (times B and C). * To get the OS overhead, compute B-A and D-C. My questions are: 1. What variable in PTLSim or QEMU should I grab that is equivalent to the rdtsc instruction? 2. Just to confirm, does the rdtsc instruction work as expected in simulation mode (i.e. it gets updated every simulated clock cycle). Thanks, Jim Stevens _______________________________________________ http://www.marss86.org Marss86-Devel mailing list [email protected] https://www.cs.binghamton.edu/mailman/listinfo/marss86-devel
