[PATCH 0/1] irqbalance: Fix min_load to pick actual min load across all objects

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On Tue, Nov 14, 2017 at 03:20:34PM -0500, Neil Horman wrote:
> 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
>

Hello Neil,

I have opened a new issue to track this bug:
https://github.com/Irqbalance/irqbalance/issues/61

Thanks.
-Vallish

> 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
> > 



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