linux-kernel - Re: MSI interrupt for xhci still lost on 5.6-rc6 after cpu hotplug

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Date:   Fri, 20 Mar 2020 10:07:26 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Evan Green <evgreen@...omium.org>
Cc:     x86@...nel.org, linux-pci <linux-pci@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Ghorai, Sukumar" <sukumar.ghorai@...el.com>,
        "Amara, Madhusudanarao" <madhusudanarao.amara@...el.com>,
        "Nandamuri, Srikanth" <srikanth.nandamuri@...el.com>
Subject: Re: MSI interrupt for xhci still lost on 5.6-rc6 after cpu hotplug

On 19.3.2020 22.24, Evan Green wrote:
> On Wed, Mar 18, 2020 at 12:23 PM Mathias Nyman
> <mathias.nyman@...ux.intel.com> wrote:
>>
>> Hi
>>
>> I can reproduce the lost MSI interrupt issue on 5.6-rc6 which includes
>> the "Plug non-maskable MSI affinity race" patch.
>>
>> I can see this on a couple platforms, I'm running a script that first generates
>> a lot of usb traffic, and then in a busyloop sets irq affinity and turns off
>> and on cpus:
>>
>> for i in 1 3 5 7; do
>>         echo "1" > /sys/devices/system/cpu/cpu$i/online
>> done
>> echo "A" > "/proc/irq/*/smp_affinity"
>> echo "A" > "/proc/irq/*/smp_affinity"
>> echo "F" > "/proc/irq/*/smp_affinity"
>> for i in 1 3 5 7; do
>>         echo "0" > /sys/devices/system/cpu/cpu$i/online
>> done
>>
>> I added some very simple debugging but I don't really know what to look for.
>> xhci interrupts (122) just stop after a setting msi affinity, it survived many
>> similar msi_set_affinity() calls before this.
>>
>> I'm not that familiar with the inner workings of this, but I'll be happy to
>> help out with adding debugging and testing patches.
> 
> How quickly are you able to reproduce this when you run your script?

Less than a minute

> Does reverting Thomas' patch make it repro faster? Can you send the
> output of lspci -vvv for the xhci device?

It's roughly the same after reverting
"6f1a4891a592 x86/apic/msi: Plug non-maskable MSI affinity race"

# lspci -vvv -d :a3af
00:14.0 USB controller: Intel Corporation Device a3af (prog-if 30 [XHCI])
        Subsystem: Intel Corporation Device 7270
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin ? routed to IRQ 122
        Region 0: Memory at b1020000 (64-bit, non-prefetchable) [size=64K]
        Capabilities: [70] Power Management version 2
                Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA PME(D0-,D1-,D2-,D3hot+,D3cold+)
                Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [80] MSI: Enable+ Count=1/8 Maskable- 64bit+
                Address: 00000000fee08000  Data: 4021
        Kernel driver in use: xhci_hcd

-Mathias