From mboxrd@z Thu Jan 1 00:00:00 1970 From: preeti@linux.vnet.ibm.com (Preeti U Murthy) Date: Mon, 02 Jun 2014 11:51:10 +0530 Subject: [PATCH v2 11/11] sched: replace capacity by activity In-Reply-To: <20140529135510.GG11074@laptop.programming.kicks-ass.net> References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org> <1400860385-14555-12-git-send-email-vincent.guittot@linaro.org> <20140529135510.GG11074@laptop.programming.kicks-ass.net> Message-ID: <538C17D6.60100@linux.vnet.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 >> --- > > 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? 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. >