linux-kernel - RE: [PATCH 1/1] scsi: storvsc: Spread interrupts when picking a channel for I/O requests

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Date:   Wed, 31 Jan 2018 21:14:26 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Long Li <longli@...rosoft.com>, KY Srinivasan <kys@...rosoft.com>,
        "Stephen Hemminger" <sthemmin@...rosoft.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>
Subject: RE: [PATCH 1/1] scsi: storvsc: Spread interrupts when picking a
 channel for I/O requests

> From: Long Li
> Sent: Wednesday, January 31, 2018 12:23 PM
> To: Michael Kelley (EOSG) <Michael.H.Kelley@...rosoft.com>; KY Srinivasan
> <kys@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>;
> martin.petersen@...cle.com; devel@...uxdriverproject.org; linux-kernel@...r.kernel.org;
> linux-scsi@...r.kernel.org; James E . J . Bottomley <jejb@...ux.vnet.ibm.com>
> Subject: RE: [PATCH 1/1] scsi: storvsc: Spread interrupts when picking a channel for I/O
> requests
> 
> > Subject: RE: [PATCH 1/1] scsi: storvsc: Spread interrupts when picking a
> > channel for I/O requests
> >
> > Updated/corrected two email addresses ...
> >
> > > -----Original Message-----
> > > From: Michael Kelley (EOSG)
> > > Sent: Wednesday, January 24, 2018 2:14 PM
> > > To: KY Srinivasan <kys@...rosoft.com>; Stephen Hemminger
> > > <sthemmin@...rosoft.com>; martin.petersen@...cle.com;
> > > longi@...rosoft.com; JBottomley@...n.com;
> > > devel@...uxdriverproject.org; linux-kernel@...r.kernel.org;
> > > linux-scsi@...r.kernel.org
> > > Cc: Michael Kelley (EOSG) <Michael.H.Kelley@...rosoft.com>
> > > Subject: [PATCH 1/1] scsi: storvsc: Spread interrupts when picking a
> > > channel for I/O requests
> > >
> > > Update the algorithm in storvsc_do_io to look for a channel starting
> > > with the current CPU + 1 and wrap around (within the current NUMA
> > > node). This spreads VMbus interrupts more evenly across CPUs. Previous
> > > code always started with first CPU in the current NUMA node, skewing
> > > the interrupt load to that CPU.
> > >
> > > Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> > > ---
> > >  drivers/scsi/storvsc_drv.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> > > index e07907d..f3264c4 100644
> > > --- a/drivers/scsi/storvsc_drv.c
> > > +++ b/drivers/scsi/storvsc_drv.c
> > > @@ -1310,7 +1310,8 @@ static int storvsc_do_io(struct hv_device *device,
> > >  			 */
> > >  			cpumask_and(&alloced_mask, &stor_device-
> > >alloced_cpus,
> > >
> > cpumask_of_node(cpu_to_node(q_num)));
> > > -			for_each_cpu(tgt_cpu, &alloced_mask) {
> > > +			for_each_cpu_wrap(tgt_cpu, &alloced_mask,
> > > +					outgoing_channel->target_cpu + 1) {
> 
> Does it work when target_cpu is the last CPU on the system?
> 
> Otherwise, looking good.

Yes, it works.  for_each_cpu_wrap() correctly wraps in the case where
the 3rd parameter ('start') is one past the end of the mask.  Arguably,
we shouldn't rely on that, and should do the wrap to 0 before calling
for_each_cpu_wrap().

> 
> > >  				if (tgt_cpu != outgoing_channel->target_cpu)
> > {
> > >  					outgoing_channel =
> > >  					stor_device->stor_chns[tgt_cpu];
> > > --
> > > 1.8.3.1