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SubjectRe: [Lse-tech] Re: [RFT PATCH] Dynamic sched domains (v0.6)
On Tue, May 17, 2005 at 10:53:54PM -0700, Paul Jackson wrote:
> Looking good. Some minor comments on these three patches ...
> * The name 'nodemask' for the cpumask_t of CPUs that are siblings to CPU i
> is a bit confusing (yes, that name was already there). How about
> something like 'siblings' ?

Not sure which code you are referring to here ?? I dont see any nodemask
referring to SMT siblings ?

> can be replaced with the one line:
> cpus_andnot(cpu_default_map, *cpu_map, cpu_isolated_map);

yeah, ok

> I would mildly prefer to always spell this 'cpu_exclusive' (with
> underscore, not hyphen).


> Good work.

Thanks !

> * Question - any idea how much of a performance hiccup a system will feel
> whenever someone changes the cpu_exclusive cpusets? Could this lead
> to a denial-of-service attack, if say some untrusted user were allowed
> modify privileges on some small cpuset that was cpu_exclusive, and they
> abused that privilege by turning on and off the cpu_exclusive property
> on their little cpuset (or creating/destroying an exclusive child):

I tried your script and see that it makes absolutely no impact on top.
The CPU on which it is running is mostly 100% idle. However I'll run
more tests to confirm that it has no impact

> * The cpuset 'oldcs' in update_flag() seems to only be used for its
> cpu_exclusive flag. We could save some stack space on my favorite
> big honkin NUMA iron by just having a local variable for this
> 'old_cpu_exclusive' value, instead of the entire cpuset.
> * Similarly, though with a bit less savings, one could replace 'oldcs'
> in update_cpumask() with just the old_cpus_allowed mask.
> Or, skip even that, and compute a boolean flag:
> cpus_changed = cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
> before copying over the trialcs, so we only need one word of stack
> for the boolean, not possibly many words for a cpumask.

ok for both

> * Non-traditional code style:
> }
> else {
> should be instead:
> } else {

I dont know how that snuck back in, I'll change that

> * Is it the case that update_cpu_domains() is called with cpuset_sem held?
> Would it be a good idea to note in the comment for that routine:
> * Call with cpuset_sem held. May nest a call to the
> * lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
> I didn't callout the cpuset_sem lock precondition on many routines,
> but since this one can nest the cpu_hotplug lock, it might be worth
> calling it out, for the benefit of engineers who are passing through,
> needing to know how the hotplug lock nests with other semaphores.


I do feel with the above updates the patches can go into -mm.
Appreciate all the review comments from everyone, Thanks

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