From: John Garry <john.garry@huawei.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>, <tglx@linutronix.de>,
<chenxiang66@hisilicon.com>, <bigeasy@linutronix.de>,
<linux-kernel@vger.kernel.org>, <hare@suse.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: Tue, 10 Dec 2019 12:05:20 +0000 [thread overview]
Message-ID: <06d1e2ff-9ec7-2262-25a0-4503cb204b0b@huawei.com> (raw)
In-Reply-To: <6e513d25d8b0c6b95d37a64df0c27b78@www.loen.fr>
On 10/12/2019 11:36, Marc Zyngier wrote:
> On 2019-12-10 10:59, John Garry wrote:
>>>>
>>>> There is no lockup, just a potential performance boost in this change.
>>>>
>>>> My colleague Xiang Chen can provide specifics of the test, as he is
>>>> the one running it.
>>>>
>>>> But one key bit of info - which I did not think most relevant before
>>>> - that is we have 2x SAS controllers running the throughput test on
>>>> the same host.
>>>>
>>>> As such, the completion queue interrupts would be spread identically
>>>> over the CPUs for each controller. I notice that ARM GICv3 ITS
>>>> interrupt controller (which we use) does not use the generic irq
>>>> matrix allocator, which I think would really help with this.
>>>>
>>>> Hi Marc,
>>>>
>>>> Is there any reason for which we couldn't utilise of the generic irq
>>>> matrix allocator for GICv3?
>>>
>>
>> Hi Marc,
>>
>>> For a start, the ITS code predates the matrix allocator by about three
>>> years. Also, my understanding of this allocator is that it allows
>>> x86 to cope with a very small number of possible interrupt vectors
>>> per CPU. The ITS doesn't have such issue, as:
>>> 1) the namespace is global, and not per CPU
>>> 2) the namespace is *huge*
>>> Now, what property of the matrix allocator is the ITS code missing?
>>> I'd be more than happy to improve it.
>>
>> I think specifically the property that the matrix allocator will try
>> to find a CPU for irq affinity which "has the lowest number of managed
>> IRQs allocated" - I'm quoting the comment on
>> matrix_find_best_cpu_managed().
>
> But that decision is due to allocation constraints. You can have at most
> 256 interrupts per CPU, so the allocator tries to balance it.
>
> On the contrary, the ITS does care about how many interrupt target any
> given CPU. The whole 2^24 interrupt namespace can be thrown at a single
> CPU.
>
>> The ITS code will make the lowest online CPU in the affinity mask the
>> target CPU for the interrupt, which may result in some CPUs handling
>> so many interrupts.
>
> If what you want is for the *default* affinity to be spread around,
> that should be achieved pretty easily. Let me have a think about how
> to do that.
Cool, I anticipate that it should help my case.
I can also seek out some NVMe cards to see how it would help a more
"generic" scenario.
Cheers,
John
next prev parent reply other threads:[~2019-12-10 12:05 UTC|newest]
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
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 [this message]
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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