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From: John Garry <john.garry@huawei.com>
To: Marc Zyngier <maz@kernel.org>
Cc: <tglx@linutronix.de>, <chenxiang66@hisilicon.com>,
	<bigeasy@linutronix.de>, <linux-kernel@vger.kernel.org>,
	<hare@suse.com>, <ming.lei@redhat.com>, <hch@lst.de>,
	<axboe@kernel.dk>, <bvanassche@acm.org>, <peterz@infradead.org>,
	<mingo@redhat.com>
Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt
Date: Fri, 6 Dec 2019 16:16:36 +0000
Message-ID: <6a004f9d-bcfd-378c-8b62-051e1f4e09b4@huawei.com> (raw)
In-Reply-To: <e44ca3b9684277bb6659b2676ef72ad8@www.loen.fr>

On 06/12/2019 15:22, Marc Zyngier wrote:

Hi Marc,

> 
> On 2019-12-06 14:35, John Garry wrote:
>> Currently the cpu allowed mask for the threaded part of a threaded irq
>> handler will be set to the effective affinity of the hard irq.
>>
>> Typically the effective affinity of the hard irq will be for a single
>> cpu. As such,
>> the threaded handler would always run on the same cpu as the hard irq.
>>
>> We have seen scenarios in high data-rate throughput testing that the cpu
>> handling the interrupt can be totally saturated handling both the hard
>> interrupt and threaded handler parts, limiting throughput.
>>
>> For when the interrupt is managed, allow the threaded part to run on all
>> cpus in the irq affinity mask.
>>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>> ---
>>  kernel/irq/manage.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> index 1753486b440c..8e7f8e758a88 100644
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -968,7 +968,11 @@ irq_thread_check_affinity(struct irq_desc *desc,
>> struct irqaction *action)
>>      if (cpumask_available(desc->irq_common_data.affinity)) {
>>          const struct cpumask *m;
>>
>> -        m = irq_data_get_effective_affinity_mask(&desc->irq_data);
>> +        if (irqd_affinity_is_managed(&desc->irq_data))
>> +            m = desc->irq_common_data.affinity;
>> +        else
>> +            m = irq_data_get_effective_affinity_mask(
>> +                    &desc->irq_data);
>>          cpumask_copy(mask, m);
>>      } else {
>>          valid = false;
> 
> Although I completely understand that there are cases where you
> really want to let your thread roam all CPUs, I feel like changing
> this based on a seemingly unrelated property is likely to trigger
> yet another whack-a-mole episode. I'd feel much more comfortable
> if there was a way to let the IRQ subsystem know about what is best.
> 
> Shouldn't the endpoint driver know better about it? 

I did propose that same idea here:
https://lore.kernel.org/lkml/fd7d6101-37f4-2d34-f2f7-cfeade610278@huawei.com/

And that fits my agenda to get best throughput figures, while not 
possibly affecting others.

But it seems that we could do better to make this a common policy: allow 
the threaded part to roam when that CPU is overloaded, but how...?

Note that
> I have no data supporting an approach or the other, hence playing
> the role of the village idiot here.
> 

Understood. My data is that we get an ~11% throughput boost for our 
storage test with this change.

> Thanks,
> 
>          M.

Thanks,
John

  reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-06 14:35 [PATCH RFC 0/1] Threaded handler uses irq affinity for when the interrupt is managed John Garry
2019-12-06 14:35 ` [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt John Garry
2019-12-06 15:22   ` Marc Zyngier
2019-12-06 16:16     ` John Garry [this message]
2019-12-07  8:03   ` Ming Lei
2019-12-09 14:30     ` John Garry
2019-12-09 15:09       ` Hannes Reinecke
2019-12-09 15:17         ` Marc Zyngier
2019-12-09 15:25           ` Hannes Reinecke
2019-12-09 15:36             ` Marc Zyngier
2019-12-09 15:49           ` Qais Yousef
2019-12-09 15:55             ` Marc Zyngier
2019-12-10  1:43       ` Ming Lei
2019-12-10  9:45         ` John Garry
2019-12-10 10:06           ` Ming Lei
2019-12-10 10:28           ` Marc Zyngier
2019-12-10 10:59             ` John Garry
2019-12-10 11:36               ` Marc Zyngier
2019-12-10 12:05                 ` John Garry
2019-12-10 18:32                   ` Marc Zyngier
2019-12-11  9:41                     ` John Garry
2019-12-13 10:07                       ` John Garry
2019-12-13 10:31                         ` Marc Zyngier
2019-12-13 12:08                           ` John Garry
2019-12-14 10:59                             ` Marc Zyngier
2019-12-11 17:09         ` John Garry
2019-12-12 22:38           ` Ming Lei
2019-12-13 11:12             ` John Garry
2019-12-13 13:18               ` Ming Lei
2019-12-13 15:43                 ` John Garry
2019-12-13 17:12                   ` Ming Lei
2019-12-13 17:50                     ` John Garry
2019-12-14 13:56                   ` Marc Zyngier
2019-12-16 10:47                     ` John Garry
2019-12-16 11:40                       ` Marc Zyngier
2019-12-16 14:17                         ` John Garry
2019-12-16 18:00                           ` Marc Zyngier
2019-12-16 18:50                             ` John Garry
2019-12-20 11:30                               ` John Garry
2019-12-20 14:43                                 ` Marc Zyngier
2019-12-20 15:38                                   ` John Garry
2019-12-20 16:16                                     ` Marc Zyngier
2019-12-20 23:31                                     ` Ming Lei
2019-12-23  9:07                                       ` Marc Zyngier
2019-12-23 10:26                                         ` John Garry
2019-12-23 10:47                                           ` Marc Zyngier
2019-12-23 11:35                                             ` John Garry
2019-12-24  1:59                                             ` Ming Lei
2019-12-24 11:20                                               ` Marc Zyngier
2019-12-25  0:48                                                 ` Ming Lei
2020-01-02 10:35                                                   ` John Garry
2020-01-03  0:46                                                     ` Ming Lei
2020-01-03 10:41                                                       ` John Garry
2020-01-03 11:29                                                         ` Ming Lei
2020-01-03 11:50                                                           ` John Garry
2020-01-04 12:03                                                             ` Ming Lei
2020-05-30  7:46 ` [tip: irq/core] irqchip/gic-v3-its: Balance initial LPI affinity across CPUs tip-bot2 for Marc Zyngier

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