Linux: Reducing Kernel Latency

With much feedback on the lkml, Ingo Molnar has continued to improve his voluntary kernel preemption patch. Testing the patch has revealed a number of areas in the 2.6 Linux kernel that were causing high latency. Fixes have been created and merged as these areas have been located. For example, following Ingo’s release of the -R6 version of the patch, Lee Revell reported that he was still able to cause measurable latencies by driving the server to swap. Ingo acknowledged that this was do to the get_swap_page() function which he described as, “pretty stupid, it does a near linear search for a free slot in the swap bitmap – this not only is a latency issue but also an overhead thing as we do it for every other page that touches swap.” He went on to add, “this is pretty much the only latency that we still having during heavy VM load”.