linux-kernel - Re: [PATCH v3 0/3] genirq/vfio: Introduce update_irq

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Date:   Tue, 20 Aug 2019 12:03:50 +0800
From:   luoben <luoben@...ux.alibaba.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        tao.ma@...ux.alibaba.com, gerry@...ux.alibaba.com,
        nanhai.zou@...ux.alibaba.com, linyunsheng@...wei.com
Subject: Re: [PATCH v3 0/3] genirq/vfio: Introduce update_irq_devid and
 optimize VFIO irq ops


在 2019/8/20 上午4:51, Alex Williamson 写道:
> On Thu, 15 Aug 2019 21:02:58 +0800
> Ben Luo <luoben@...ux.alibaba.com> wrote:
>
>> Currently, VFIO takes a lot of free-then-request-irq actions whenever
>> a VM (with device passthru via VFIO) sets irq affinity or mask/unmask
>> irq. Those actions only change the cookie data of irqaction or even
>> change nothing. The free-then-request-irq not only adds more latency,
>> but also increases the risk of losing interrupt, which may lead to a
>> VM hung forever in waiting for IO completion
> What guest environment is generating this?  Typically I don't see that
> Windows or Linux guests bounce the interrupt configuration much.
> Thanks,
>
> Alex

By tracing centos5u8 on host, I found it keep masking and unmasking 
interrupt like this:

[1566032533709879] index:28 irte_hi:000000010004a601 
irte_lo:adb54bc000b98001
[1566032533711242] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533711258] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533711269] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533711291] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533711321] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533711340] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533711361] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533711376] index:28 irte_hi:000000010004a601 
irte_lo:adb54bc000b98001
[1566032533713368] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533713385] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533713396] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533713416] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533713447] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533713464] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533713485] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533713499] index:28 irte_hi:000000010004a601 
irte_lo:adb54bc000b98001
[1566032533718855] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533718871] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533718882] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533718902] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533718932] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533718949] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533718969] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533718984] index:28 irte_hi:000000010004a601 
irte_lo:adb54bc000b98001
[1566032533719873] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533719889] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533719900] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533719921] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533719954] index:28 irte_hi:0000000000000000 
irte_lo:0000000000000000
[1566032533719971] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533719992] index:28 irte_hi:000000000004a601 
irte_lo:00003fff00ac002d
[1566032533720007] index:28 irte_hi:000000010004a601 
irte_lo:adb54bc000b98001

"[1566032533720007]" is timestamp in μs, so centos5u8 tiggers 30+ irte 
modification within 10ms

Thanks,

     Ben

>> This patchset solved the issue by:
>> Patch 2 introduces update_irq_devid to only update dev_id of irqaction
>> Patch 3 make use of update_irq_devid and optimize irq operations in VFIO
>>
>> changes from v2:
>>   - reformat to avoid quoted string split across lines and etc.
>>
>> changes from v1:
>>   - add Patch 1 to enhance error recovery etc. in free irq per tglx's comments
>>   - enhance error recovery code and debugging info in update_irq_devid
>>   - use __must_check in external referencing of update_irq_devid
>>   - use EXPORT_SYMBOL_GPL for update_irq_devid
>>   - reformat code of patch 3 for better readability
>>
>> Ben Luo (3):
>>    genirq: enhance error recovery code in free irq
>>    genirq: introduce update_irq_devid()
>>    vfio_pci: make use of update_irq_devid and optimize irq ops
>>
>>   drivers/vfio/pci/vfio_pci_intrs.c | 101 +++++++++++++++++++++-------------
>>   include/linux/interrupt.h         |   3 ++
>>   kernel/irq/manage.c               | 110 +++++++++++++++++++++++++++++++++-----
>>   3 files changed, 164 insertions(+), 50 deletions(-)
>>