linux-kernel - Re: [Patch v1 2/3] PCI: prevent work_on_cpu's probe to execute on isolated CPUs

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Date:   Wed, 17 Jun 2020 01:22:18 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        mtosatti@...hat.com, juri.lelli@...hat.com, abelits@...vell.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        rostedt@...dmis.org, mingo@...nel.org, peterz@...radead.org,
        tglx@...utronix.de
Subject: Re: [Patch v1 2/3] PCI: prevent work_on_cpu's probe to execute on
 isolated CPUs

On Wed, Jun 10, 2020 at 12:12:25PM -0400, Nitesh Narayan Lal wrote:
> From: Alex Belits <abelits@...vell.com>
> 
> pci_call_probe() prevents the nesting of work_on_cpu()
> for a scenario where a VF device is probed from work_on_cpu()
> of the Physical device.
> This patch replaces the cpumask used in pci_call_probe()
> from all online CPUs to only housekeeping CPUs. This is to
> ensure that there are no additional latency overheads
> caused due to the pinning of jobs on isolated CPUs.
> 
> Signed-off-by: Alex Belits <abelits@...vell.com>
> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
> ---
>  drivers/pci/pci-driver.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index da6510af1221..449466f71040 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -12,6 +12,7 @@
>  #include <linux/string.h>
>  #include <linux/slab.h>
>  #include <linux/sched.h>
> +#include <linux/sched/isolation.h>
>  #include <linux/cpu.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/suspend.h>
> @@ -333,6 +334,7 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
>  			  const struct pci_device_id *id)
>  {
>  	int error, node, cpu;
> +	int hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ;
>  	struct drv_dev_and_id ddi = { drv, dev, id };
>  
>  	/*
> @@ -353,7 +355,8 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
>  	    pci_physfn_is_probed(dev))
>  		cpu = nr_cpu_ids;
>  	else
> -		cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
> +		cpu = cpumask_any_and(cpumask_of_node(node),
> +				      housekeeping_cpumask(hk_flags));

Looks like cpumask_of_node() is based on online CPUs. So that all
looks good. Thanks!

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>


>  
>  	if (cpu < nr_cpu_ids)
>  		error = work_on_cpu(cpu, local_pci_probe, &ddi);
> -- 
> 2.18.4
>