On 2 June 2014 08:21, Preeti U Murthy <pre...@linux.vnet.ibm.com> wrote: > On 05/29/2014 07:25 PM, Peter Zijlstra wrote: >> On Fri, May 23, 2014 at 05:53:05PM +0200, Vincent Guittot wrote: >>> The scheduler tries to compute how many tasks a group of CPUs can handle by >>> assuming that a task's load is SCHED_LOAD_SCALE and a CPU capacity is >>> SCHED_POWER_SCALE. >>> We can now have a better idea of the utilization of a group fo CPUs thanks >>> to >>> group_actitvity and deduct how many capacity is still available. >>> >>> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> >>> --- >> >> Right, so as Preeti already mentioned, this wrecks SMT. It also seems to >> loose the aggressive spread, where we want to run 1 task on each 'core' >> before we start 'balancing'. > > True. I just profiled the ebizzy runs and found that ebizzy threads were > being packed onto a single core which is SMT-8 capable before spreading. > This was a 6 core, SMT-8 machine. So for instance if I run 8 threads of > ebizzy. the load balancing as record by perf sched record showed that > two cores were packed upto 3 ebizzy threads and one core ran two ebizzy > threads while the rest of the 3 cores were idle. > > I am unable to understand which part of this patch is aiding packing to > a core. There is this check in this patch right? > > if (sgs->group_capacity < 0) > return true; > > which should ideally prevent such packing? Because irrespective of the > number of SMT threads, the capacity of a core is unchanged. And in the > above scenario, we have 6 tasks on 3 cores. So shouldn't the above check > have caught it?
yes, it should. the group_capacity should become < 0 because the CPU are fully loaded and the activity reach the max capacity value + nr_running > > Regards > Preeti U Murthy >> >> So I think we should be able to fix this by setting PREFER_SIBLING on >> the SMT domain, that way we'll get single tasks running on each SMT >> domain before filling them up until capacity. >> >> Now, its been a while since I looked at PREFER_SIBLING, and I've not yet >> looked at what your patch does to it, but it seems to me that that is >> the first direction we should look for an answer to this. >> > -- 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/
