On Wed, Oct 29, 2014 at 12:48:34PM +0000, Matt Fleming wrote: > On Wed, 29 Oct, at 09:16:40AM, Peter Zijlstra wrote: > > > > Ah, so one way around that is to only assign a (whats the CQE equivalent > > of RMIDs again?) once you stick a task in. > > I think you're after "Class of Service" (CLOS) ID. > > Yeah we can do the CLOS ID assignment on-demand but what we can't do > on-demand is the cache bitmask assignment, i.e. how we carve up the LLC. > These need to persist irrespective of which task is running. And it's > the cache bitmask that I'm specifically talking about not allowing > arbitrarly deep nesting. > > So if I create a cgroup directory with a mask of 0x3 in the root cgroup > directory for CAT (meow).
All we now need is a DOG to go woof :-) and they can have a party. > Then, create two sub-directories, and split my > 0x3 bitmask into 0x2 and 0x1, it's impossible to nest any further, i.e. > > /sys/fs/cgroup/cacheqe 0xffffffff > | > | > meow 0x3 > / \ > / \ > sub1 sub2 0x1, 0x2 > > Of course the pathological case is creating a cgroup directory with > bitmask 0x1, so you can't have sub-directories because you can't split > the cache allocation at all. > > Does this fly in the face of "full hierarchies"? Or is this a reasonable > limitation? I don't see a reason why we should not allow further children of sub1, they'll all have to have 0x1, but that should be fine, pointless perhaps, but perfectly consistent. > > But basically it means you need to allow things like: > > > > root/virt/more/crap/hostA > > /hostB > > /sanityA > > /random/other/yunk > > > > Now, the root will have the entire bitmask set, any child, say > > virt/more/crap can also have them all set, and you can maybe only start > > differentiating in the /host[AB] bits. > > > > Whether or not it makes sense, libvirt likes to create these pointless > > deep hierarchies, as do a lot of other people for that matter. > > OK, this is something I hadn't considered; that you may *not* want to > split the cache bitmask as you move down the hierarchy. > > I think that's something we could do without too much pain, though > actually programming that from a user perspective makes my head hurt. Right, also note that in the libvirt case, most of the intermediate groups are empty (of tasks) and would thus not actually instantiate a CLOS thingy. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/