Messages in this thread | | | Date | Mon, 21 Dec 2015 10:48:22 -0500 | From | Luiz Capitulino <> | Subject | Re: [PATCH V16 11/11] x86,cgroup/intel_rdt : Add a cgroup interface to manage Intel cache allocation |
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On Sat, 19 Dec 2015 22:57:30 -0200 Marcelo Tosatti <mtosatti@redhat.com> wrote:
> On Sat, Dec 19, 2015 at 11:42:57AM +0100, Thomas Gleixner wrote: > > On Thu, 17 Dec 2015, Fenghua Yu wrote: > > > > > From: Fenghua Yu <fenghua.yu@intel.com> > > > > > > From: Vikas Shivappa <vikas.shivappa@linux.intel.com> > > > > > > Add a new cgroup 'intel_rdt' to manage cache allocation. Each cgroup > > > directory is associated with a class of service id(closid). To map a > > > task with closid during scheduling, this patch removes the closid field > > > from task_struct and uses the already existing 'cgroups' field in > > > task_struct. > > > > > > The cgroup has a file 'l3_cbm' which represents the L3 cache capacity > > > bitmask(CBM). The CBM is global for the whole system currently. The > > > capacity bitmask needs to have only contiguous bits set and number of > > > bits that can be set is less than the max bits that can be set. The > > > tasks belonging to a cgroup get to fill in the L3 cache represented by > > > the capacity bitmask of the cgroup. For ex: if the max bits in the CBM > > > is 10 and the cache size is 10MB, each bit represents 1MB of cache > > > capacity. > > > > > > Root cgroup always has all the bits set in the l3_cbm. User can create > > > more cgroups with mkdir syscall. By default the child cgroups inherit > > > the capacity bitmask(CBM) from parent. User can change the CBM specified > > > in hex for each cgroup. Each unique bitmask is associated with a class > > > of service ID and an -ENOSPC is returned once we run out of > > > closids. > > > > This is still the original crap. No, we are not introducing this > > interface now just because we can. I explained in great length why > > this is completely useless and what we really need. > > > > Thanks, > > > > tglx > > Can you make a summary of the points, and enumerate them, please. > (what are the problems of the current interface, and why such problems > are fixed in the new interface?).
Marcelo, you participated on the discussions. We discussed why this is a bad interface a *lot* in the v15 posting. There are two writeups that summarize all the problems:
- https://lkml.org/lkml/2015/11/18/637
- http://lkml.iu.edu/hypermail/linux/kernel/1511.0/02375.html
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