On Tue, Nov 14, 2017 at 07:20:33PM +0000, Vallish Vaidyeshwara wrote: > We recently encountered a corner case bug in irqbalance where irqbalance > was not balancing interrupts across 2 CPU's. > We've moved to github: https://github.com/Irqbalance/irqbalance If you wouldn't mind opening a pull request or an issue for this, we can happily take a look at it there Best Neil > The code snippet in question is: > static void gather_load_stats(struct topo_obj *obj, void *data) > { > struct load_balance_info *info = data; > > if (info->min_load == 0 || obj->load < info->min_load) > info->min_load = obj->load; > info->total_load += obj->load; > info->load_sources += 1; > } > > The bug we encountered had 2 CPU's with load for the first CPU being 0. > Eg: obj1->load = 0 and obj2->load = 5000. > > Iteration 1: obj1 is passed and info initialized to 0 is passed in > as param. > if (info->min_load == 0 || obj->load < info->min_load) > info->min_load = obj->load; > Because info->min_load is 0, info->min_load is set to obj->load which > is also 0 in this case. > > Iteration 2: obj2 is passed with info having values set from previous > iteration: > info->min_load = 0, info->total_load = 0, info->load_sources = 1 > > if (info->min_load == 0 || obj->load < info->min_load) > info->min_load = obj->load; > Because of the logic used in gather_load_stats() as shown above, > info->min_load gets set to obj2->load which is 5000. This is not the > minimum load. Because of this bug, interrupts do not migrate as this > value is checked in the function which migrates the interrupts. > > Test results: > ------------- > i3.large system - single socket, single core, hyperthreading enabled > > With fix: > [ec2-user at ip-10-0-38-254 tmp]$ cat /proc/interrupts | grep "\<CPU0\>\|\<60\>\|\<61\>\|\<66\>\|\<67\>\|\<69\>\|\<70\>" > CPU0 CPU1 > 60: 1593819 292297 xen-pirq-msi-x nvme0q0, nvme0q1 > 61: 456537 831877 xen-pirq-msi-x nvme0q2 > 66: 1498 1644 xen-pirq-msi-x eth1-Tx-Rx-0 > 67: 1535 1034 xen-pirq-msi-x eth1-Tx-Rx-1 > 69: 3579919 8973629 xen-pirq-msi-x eth2-Tx-Rx-0 > 70: 9265764 3747096 xen-pirq-msi-x eth2-Tx-Rx-1 > > Without fix: > [ec2-user at ip-10-0-10-75 ~]$ cat /proc/interrupts | grep "\<CPU0\>\|\<60\>\|\<61\>\|\<66\>\|\<67\>\|\<69\>\|\<70\>" > CPU0 CPU1 > 60: 4014 1088758 xen-pirq-msi-x nvme0q0, nvme0q1 > 61: 2046 2218741 xen-pirq-msi-x nvme0q2 > 66: 11 2978 xen-pirq-msi-x eth1-Tx-Rx-0 > 67: 8 43 xen-pirq-msi-x eth1-Tx-Rx-1 > 69: 43 13773325 xen-pirq-msi-x eth2-Tx-Rx-0 > 70: 4 13102621 xen-pirq-msi-x eth2-Tx-Rx-1 > > Vallish Vaidyeshwara (1): > irqbalance: Fix min_load to pick actual min load across all objects > > irqlist.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > -- > 2.7.5 > > > _______________________________________________ > irqbalance mailing list > irqbalance at lists.infradead.org > http://lists.infradead.org/mailman/listinfo/irqbalance >
