linux-kernel - Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt

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Message-ID: <2443e657-2ccd-bf85-072c-284ea0b3ce40@huawei.com>
Date:   Fri, 13 Dec 2019 10:07:21 +0000
From:   John Garry <john.garry@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Ming Lei <ming.lei@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "chenxiang (M)" <chenxiang66@...ilicon.com>,
        "bigeasy@...utronix.de" <bigeasy@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hare@...e.com" <hare@...e.com>, "hch@....de" <hch@....de>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "bvanassche@....org" <bvanassche@....org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>
Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity
 for managed interrupt

On 11/12/2019 09:41, John Garry wrote:
> On 10/12/2019 18:32, Marc Zyngier wrote:
>>>>> 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.
>> Can you give the following a go? It probably has all kind of warts on
>> top of the quality debug information, but I managed to get my D05 and
>> a couple of guests to boot with it. It will probably eat your data,
>> so use caution!;-)
>>
> 
> Hi Marc,
> 
> Ok, we'll give it a spin.
> 
> Thanks,
> John

Hi Marc,

JFYI, we're still testing this and the patch itself seems to work as 
intended.

Here's the kernel log if you just want to see how the interrupts are 
getting assigned:
https://pastebin.com/hh3r810g

For me, I did get a performance boost for NVMe testing, but my colleague 
Xiang Chen saw a drop for our storage test of interest  - that's the 
HiSi SAS controller. We're trying to make sense of it now.

Thanks,
John

> 
>> Thanks,
>>
>>           M.
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c
>> b/drivers/irqchip/irq-gic-v3-its.c
>> index e05673bcd52b..301ee3bc0602 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -177,6 +177,8 @@ static DEFINE_IDA(its_vpeid_ida);
>