KernelTrap: Reducing Kernel Latency
Sep 14, 2004, 02:30 (0 Talkback[s])
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"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...'"