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

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Message-ID: <Z32t88W3biaZa7fH@yury-ThinkPad>
Date: Tue, 7 Jan 2025 14:42:59 -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 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?

> 
> >  	/* set queue affinity mask */
> >  	cpumask_copy(queue->affinity_mask, mask);
> >  	rc = irq_set_affinity_and_hint(queue->irq, queue->affinity_mask);
> > @@ -256,7 +261,7 @@ static void ibmvnic_set_affinity(struct ibmvnic_adapter *adapter)
> >  	int num_rxqs = adapter->num_active_rx_scrqs, i_rxqs = 0;
> >  	int num_txqs = adapter->num_active_tx_scrqs, i_txqs = 0;
> >  	int total_queues, stride, stragglers, i;
> > -	unsigned int num_cpu, cpu;
> > +	unsigned int num_cpu, cpu = 0;
> >  	bool is_rx_queue;
> >  	int rc = 0;
> >  
> > @@ -274,8 +279,6 @@ static void ibmvnic_set_affinity(struct ibmvnic_adapter *adapter)
> >  	stride = max_t(int, num_cpu / total_queues, 1);
> >  	/* number of leftover cpu's */
> >  	stragglers = num_cpu >= total_queues ? num_cpu % total_queues : 0;
> > -	/* next available cpu to assign irq to */
> > -	cpu = cpumask_next(-1, cpu_online_mask);
> >  
> >  	for (i = 0; i < total_queues; i++) {
> >  		is_rx_queue = false;
> > -- 
> > 2.43.0
> >