>>> On Tue, Jan 29, 2008 at 6:30 AM, in message <[EMAIL PROTECTED]>, Paul Jackson <[EMAIL PROTECTED]> wrote: > Peter wrote, in reply to Peter ;): >> > [ It looks to me it balances a group over the largest SD the current cpu >> > has access to, even though that might be larger than the SD associated >> > with the cpuset of that particular cgroup. ] >> >> Hmm, with a bit more thought I think that does indeed DTRT. Because, if >> the cpu belongs to a disjoint cpuset, the highest sd (with >> load-balancing enabled) would be that. Right? > > The code that defines sched domains, kernel/sched.c > partition_sched_domains(), > as called from the cpuset code in kernel/cpuset.c rebuild_sched_domains(), > does not make use of the full range of sched_domain possibilities. > > In particular, it only sets up some non-overlapping set of sched domains. > Every CPU ends up in at most a single sched domain. > > The original reason that one can't define overlapping sched domains via > this cpuset interface (based off the cpuset 'sched_load_balance' flag) > is that I didn't realize it was even possible to overlap sched domains > when I wrote the cpuset code defining sched domains. And then when I > later realized one could overlap sched domains, I (a) didn't see a need > to do so, and (b) couldn't see how to do so via the cpuset interface > without causing my brain to explode. > > Now, back to Peter's question, being a bit pedantic, CPUs don't belong > to disjoint cpusets, except in the most minimal situation that there is > only one cpuset covering all CPUs. > > Rather what happens, when you have need for some realtime CPUs, is that: > 1) you turn off sched_load_balance on the top cpuset, > 2) you setup your realtime cpuset as a child cpuset of the top cpuset > such that its CPUs doesn't overlap any of its siblings, and > 3) you turn off sched_load_balance in that realtime cpuset. > > At that point, sched domains are rebuilt, including providing a > sched domain that just contains the CPUs in that realtime cpuset, and > normal scheduler load balancing ceases on the CPUs in that realtime > cpuset.
Hi Paul, I am a bit confused as to why you disable load-balancing in the RT cpuset? It shouldn't be strictly necessary in order for the RT scheduler to do its job (unless I am misunderstanding what you are trying to accomplish?). Do you do this because you *have* to in order to make real-time deadlines, or because its just a further optimization? -Greg > >> [ Just a bit of a shame we have all cgroups represented on each cpu. ] > > Could you restate this -- I suspect it's obvious, but I'm oblivious ;). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
