netdev - Re: [PATCH v4 3/5] net: mana: explain irq

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Message-ID: <20250529131522.GA27681@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Thu, 29 May 2025 06:15:22 -0700
From: Shradha Gupta <shradhagupta@...ux.microsoft.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Dexuan Cui <decui@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Konstantin Taranov <kotaranov@...rosoft.com>,
	Simon Horman <horms@...nel.org>, Leon Romanovsky <leon@...nel.org>,
	Maxim Levitsky <mlevitsk@...hat.com>,
	Erni Sri Satya Vennela <ernis@...ux.microsoft.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Kelley <mhklinux@...look.com>, linux-hyperv@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nipun Gupta <nipun.gupta@....com>, Jason Gunthorpe <jgg@...pe.ca>,
	Jonathan Cameron <Jonathan.Cameron@...ei.com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Kevin Tian <kevin.tian@...el.com>, Long Li <longli@...rosoft.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczy???~Dski <kw@...ux.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, Paul Rosswurm <paulros@...rosoft.com>,
	Shradha Gupta <shradhagupta@...rosoft.com>
Subject: Re: [PATCH v4 3/5] net: mana: explain irq_setup() algorithm

On Tue, May 27, 2025 at 03:10:15PM -0400, Yury Norov wrote:
> So now git will think that you're the author of the patch.
> 
> If author and sender are different people, the first line in commit
> message body should state that. In this case, it should be:
> 
> From: Yury Norov <yury.norov@...il.com>
> 
> Please consider this one example
> 
> https://patchew.org/linux/20250326-fixed-type-genmasks-v8-0-24afed16ca00@wanadoo.fr/20250326-fixed-type-genmasks-v8-6-24afed16ca00@wanadoo.fr/
> 
> Thanks,
> Yury
>

Understood, Thank you Yury. I'll make this change in the next version

Regards,
Shradha. 
> On Tue, May 27, 2025 at 08:58:25AM -0700, Shradha Gupta wrote:
> > Commit 91bfe210e196 ("net: mana: add a function to spread IRQs per CPUs")
> > added the irq_setup() function that distributes IRQs on CPUs according
> > to a tricky heuristic. The corresponding commit message explains the
> > heuristic.
> > 
> > Duplicate it in the source code to make available for readers without
> > digging git in history. Also, add more detailed explanation about how
> > the heuristics is implemented.
> > 
> > Signed-off-by: Yury Norov [NVIDIA] <yury.norov@...il.com>
> > Signed-off-by: Shradha Gupta <shradhagupta@...ux.microsoft.com>
> > ---
> >  .../net/ethernet/microsoft/mana/gdma_main.c   | 41 +++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > index 4ffaf7588885..f9e8d4d1ba3a 100644
> > --- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > +++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > @@ -1288,6 +1288,47 @@ void mana_gd_free_res_map(struct gdma_resource *r)
> >  	r->size = 0;
> >  }
> >  
> > +/*
> > + * Spread on CPUs with the following heuristics:
> > + *
> > + * 1. No more than one IRQ per CPU, if possible;
> > + * 2. NUMA locality is the second priority;
> > + * 3. Sibling dislocality is the last priority.
> > + *
> > + * Let's consider this topology:
> > + *
> > + * Node            0               1
> > + * Core        0       1       2       3
> > + * CPU       0   1   2   3   4   5   6   7
> > + *
> > + * The most performant IRQ distribution based on the above topology
> > + * and heuristics may look like this:
> > + *
> > + * IRQ     Nodes   Cores   CPUs
> > + * 0       1       0       0-1
> > + * 1       1       1       2-3
> > + * 2       1       0       0-1
> > + * 3       1       1       2-3
> > + * 4       2       2       4-5
> > + * 5       2       3       6-7
> > + * 6       2       2       4-5
> > + * 7       2       3       6-7
> > + *
> > + * The heuristics is implemented as follows.
> > + *
> > + * The outer for_each() loop resets the 'weight' to the actual number
> > + * of CPUs in the hop. Then inner for_each() loop decrements it by the
> > + * number of sibling groups (cores) while assigning first set of IRQs
> > + * to each group. IRQs 0 and 1 above are distributed this way.
> > + *
> > + * Now, because NUMA locality is more important, we should walk the
> > + * same set of siblings and assign 2nd set of IRQs (2 and 3), and it's
> > + * implemented by the medium while() loop. We do like this unless the
> > + * number of IRQs assigned on this hop will not become equal to number
> > + * of CPUs in the hop (weight == 0). Then we switch to the next hop and
> > + * do the same thing.
> > + */
> > +
> >  static int irq_setup(unsigned int *irqs, unsigned int len, int node)
> >  {
> >  	const struct cpumask *next, *prev = cpu_none_mask;
> > -- 
> > 2.34.1