The configurable timer interrupt frequency patch, part of the 2.6.13
kernel, led to a certain amount of controversy over the optimal default
value. That default is 250 Hz, but there arguments in favor of both
increasing and decreasing that value. There was no consensus on what the
default should really be, but there is
a certain amount of agreement
that the real solution is to merge the dynamic
. By varying the timer interrupt frequency in response to
the actual system workload, the dynamic tick approach should be able to
satisfy most users.
Now that patches are being merged for 2.6.14, the obvious question came up:
will dynamic tick be one of them? The answer, it seems, is almost
certainly "no." This patch, despite being around in one form or another
for years, is still not quite ready.
One issue, apparently, is that systems running with dynamic tick tend to
boot slowly, and nobody has yet figured out why. The problem can be masked
by simply waiting until the system has booted before turning on dynamic
tick, but that solution appeals to nobody. Until this behavior is
understood, there will almost certainly be opposition to the merging of
Another problem with the current patch is that it does not work
particularly well on SMP systems. It requires that all CPUs go idle
before the timer interrupt frequency can be reduced. But an SMP system may
well have individual CPUs with no work to do while others are busy; such a
situation could come up fairly often. Srivatsa Vaddagiri is working on a patch for SMP systems, but it is still a
work in progress and has not received widespread testing.
The end result is that dynamic tick is unlikely to come together in time to
get into 2.6.14; the window for merging of patches of this magnitude is
supposed to close within a week or so. So this patch will be for 2.6.15 at
the earliest. If the revised development process works as planned, 2.6.15
should not be all that far away. Hopefully.
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