On Thursday 08 February 2007 20:01, Michael Gagnon wrote: > Hello. I'm a student at George Mason University and I had a question > regarding the time complexity of QEMU's algorithm for dealing with > self-modifying code. > > From looking at the QEMU Internals documentation > (http://fabrice.bellard.free.fr/qemu/qemu-tech.html), it seems that > QEMU's method for handling self-modifying code might have different > algorithmic efficiency classes for it's average case and worst case. As > in, on average I assume that QEMU emulates instructions at O(n) > efficiency. In the worst-case, might self-modifying code change the > efficiency of QEMU to another order of efficiency, such as O(n^2)? Any > thoughts would be greatly appreciated. Thanks!
Depends what your N is. Worst case for SMC (Self Modifying Code) is modifying code in the same TB (Translation Block) as the store instruction. This kind of fault requires O(tb_size) time, so executing a TB (assuming every insn traps) takes O(tb_size ^2) time. However the page boundaries impose a hard limit on the size of a TB. Thus for N < TARGET_PAGE_SIZE worst case total execution time is O(N^2), but for N > TARGET_PAGE_SIZE total execution time is still O(N). For SMC the constant factor may be orders of magnitude larger than for regular code. Paul _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
