Make it possible to have interactivity and responsiveness at very high load
levels by making deadlines offset by the fork depth from init. This has a
similar effect to 'nice'ing loads that are fork heavy. 'make' is a perfect
example of this and will, with fork_depth_penalty enabled, be felt as much
at 'make -j24' as it normally would be with just 'make'.
Note that this drastically affects CPU distribution, and also has the
indirect side effect of partitioning CPU entitlement to different users as
well. No assumption as to CPU distribution should be made based on past
This is achieved by separating out forks to new processes vs new threads.
When a new process is detected, its fork depth is inherited from its parent
across fork() and then is incremented by one. That fork_depth is then used
to cause a relative offset of its deadline.
This feature is enabled in this patch by default and can be optionally
Threads are kept at the same fork_depth as their parent process, and can
optionally have their CPU entitlement all managed as one process together
by enabling the group_thread_accounting feature. This feature is disabled
by default in this patch, as many desktop applications such as firefox,
amarok, etc are multithreaded. By disabling this feature and enabling the
fork_depth_penalty feature (default) it favours CPU towards desktop
Extensive testing is required to ensure this does not cause regressions in
There are two sysctls to enable/disable these features.
They are in /proc/sys/kernel/
group_thread_accounting - groups CPU accounting by threads
fork_depth_penalty - penalises according to depth of forking from init
An updated patch for 2.6.36-rc7-ck1 follows, though it should apply to a BFS357 patched kernel with offsets:
EDIT: Here is a patch that can be applied to vanilla 18.104.22.168 which gives you BFS + this change:
EDIT2: I notice some people are trying this patch and the earlier released group as entities patch and trying to compare them. Let me make it clear, this patch REPLACES the group as entities patch and does exactly the same thing, only updated.
I am still after feedback on this approach as for my workloads it's only advantageous so I'd love it if more people would report back their experiences, either in the comments here or via email to me at firstname.lastname@example.org . Thanks!