linux-kernel - Re: [PATCH 03/14] ibmvnic: simplify ibmvnic_set_queue

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Message-ID: <Z32zCDd2GnFPW465@yury-ThinkPad>
Date: Tue, 7 Jan 2025 15:04:40 -0800
From: Yury Norov <yury.norov@...il.com>
To: Nick Child <nnac123@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, Haren Myneni <haren@...ux.ibm.com>,
	Rick Lindsley <ricklind@...ux.ibm.com>,
	Thomas Falcon <tlfalcon@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 03/14] ibmvnic: simplify ibmvnic_set_queue_affinity()

On Tue, Jan 07, 2025 at 02:43:01PM -0800, Yury Norov wrote:
> On Tue, Jan 07, 2025 at 04:37:17PM -0600, Nick Child wrote:
> > On Sat, Dec 28, 2024 at 10:49:35AM -0800, Yury Norov wrote:
> > > A loop based on cpumask_next_wrap() opencodes the dedicated macro
> > > for_each_online_cpu_wrap(). Using the macro allows to avoid setting
> > > bits affinity mask more than once when stride >= num_online_cpus.
> > > 
> > > This also helps to drop cpumask handling code in the caller function.
> > > 
> > > Signed-off-by: Yury Norov <yury.norov@...il.com>
> > > ---
> > >  drivers/net/ethernet/ibm/ibmvnic.c | 17 ++++++++++-------
> > >  1 file changed, 10 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
> > > index e95ae0d39948..4cfd90fb206b 100644
> > > --- a/drivers/net/ethernet/ibm/ibmvnic.c
> > > +++ b/drivers/net/ethernet/ibm/ibmvnic.c
> > > @@ -234,11 +234,16 @@ static int ibmvnic_set_queue_affinity(struct ibmvnic_sub_crq_queue *queue,
> > >  		(*stragglers)--;
> > >  	}
> > >  	/* atomic write is safer than writing bit by bit directly */
> > > -	for (i = 0; i < stride; i++) {
> > > -		cpumask_set_cpu(*cpu, mask);
> > > -		*cpu = cpumask_next_wrap(*cpu, cpu_online_mask,
> > > -					 nr_cpu_ids, false);
> > > +	for_each_online_cpu_wrap(i, *cpu) {
> > > +		if (!stride--)
> > > +			break;
> > > +		cpumask_set_cpu(i, mask);
> > >  	}
> > > +
> > > +	/* For the next queue we start from the first unused CPU in this queue */
> > > +	if (i < nr_cpu_ids)
> > > +		*cpu = i + 1;
> > > +
> > This should read '*cpu = i'. Since the loop breaks after incrementing i.
> > Thanks!
> 
> cpumask_next_wrap() makes '+ 1' for you. The for_each_cpu_wrap() starts
> exactly where you point. So, this '+1' needs to be explicit now.
> 
> Does that make sense?

Ah, I think I see what you mean. It should be like this, right?

  for_each_online_cpu_wrap(i, *cpu) {
  	if (!stride--) {
        	*cpu = i + 1;
  		break;
        }
  	cpumask_set_cpu(i, mask);
  }