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

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Message-ID: <562ce033-50d6-37f0-57a6-de3dd6623c5c@redhat.com>
Date:   Tue, 16 Jun 2020 18:03:14 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        frederic@...nel.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 6/16/20 4:05 PM, Bjorn Helgaas wrote:
> "git log --oneline drivers/pci/pci-driver.c" tells you that the
> subject should be something like:
>
>   PCI: Restrict probe functions to housekeeping 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.
> s/Physical/PF/ (since you used "VF" earlier, this should match that)
>
> s/This patch replaces/Replace the/
>
> Please rewrap this to fill a 75 column line (so it doesn't overflow 80
> columns when "git log" adds 4 spaces).
>
> This should be two paragraphs; add a blank line between them.

Thanks for pointing these out.
I will correct it in the next posting before that I will wait for any comments
on other patches.

>
>> Signed-off-by: Alex Belits <abelits@...vell.com>
>> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.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));
>>  
>>  	if (cpu < nr_cpu_ids)
>>  		error = work_on_cpu(cpu, local_pci_probe, &ddi);
>> -- 
>> 2.18.4
>>
-- 
Nitesh



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