Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node

[John Garry]

On 22/07/2021 11:19, Ming Lei wrote:
> > If you check below, you can see that cpu4 services an NVMe irq. From
> > checking htop, during the test that cpu is at 100% load, which I put the
> > performance drop (vs cpu0) down to.
> nvme.poll_queues is 2 in my test, and no irq is involved. But the irq mode
> fio test is still as bad as io_uring.

I tried that:

dmesg | grep -i nvme
[    0.000000] Kernel command line: BOOT_IMAGE=/john/Image rdinit=/init 
crashkernel=256M@32M console=ttyAMA0,115200 earlycon acpi=force 
pcie_aspm=off noinitrd root=/dev/sda1 rw log_buf_len=16M user_debug=1 
iommu.strict=1 nvme.use_threaded_interrupts=0 irqchip.gicv3_pseudo_nmi=1 
nvme.poll_queues=2

[   30.531989] megaraid_sas 0000:08:00.0: NVMe passthru support : Yes
[   30.615336] megaraid_sas 0000:08:00.0: NVME page size   : (4096)
[   52.035895] nvme 0000:81:00.0: Adding to iommu group 5
[   52.047732] nvme nvme0: pci function 0000:81:00.0
[   52.067216] nvme nvme0: 22/0/2 default/read/poll queues
[   52.087318]  nvme0n1: p1

So I get these results:
cpu0 335K
cpu32 346K
cpu64 300K
cpu96 300K

So still not massive changes.

> > Here's some system info:
> >
> > HW queue irq affinities:
> > PCI name is 81:00.0: nvme0n1
> > -eirq 298, cpu list 67, effective list 67
> > -eirq 299, cpu list 32-38, effective list 35
> > -eirq 300, cpu list 39-45, effective list 39
> > -eirq 301, cpu list 46-51, effective list 46
> > -eirq 302, cpu list 52-57, effective list 52
> > -eirq 303, cpu list 58-63, effective list 60
> > -eirq 304, cpu list 64-69, effective list 68
> > -eirq 305, cpu list 70-75, effective list 70
> > -eirq 306, cpu list 76-80, effective list 76
> > -eirq 307, cpu list 81-85, effective list 84
> > -eirq 308, cpu list 86-90, effective list 86
> > -eirq 309, cpu list 91-95, effective list 92
> > -eirq 310, cpu list 96-101, effective list 100
> > -eirq 311, cpu list 102-107, effective list 102
> > -eirq 312, cpu list 108-112, effective list 108
> > -eirq 313, cpu list 113-117, effective list 116
> > -eirq 314, cpu list 118-122, effective list 118
> > -eirq 315, cpu list 123-127, effective list 124
> > -eirq 316, cpu list 0-5, effective list 4
> > -eirq 317, cpu list 6-11, effective list 6
> > -eirq 318, cpu list 12-16, effective list 12
> > -eirq 319, cpu list 17-21, effective list 20
> > -eirq 320, cpu list 22-26, effective list 22
> > -eirq 321, cpu list 27-31, effective list 28
> >
> >
> > john@ubuntu:~$ lscpu | grep NUMA
> > NUMA node(s):  4
> > NUMA node0 CPU(s):   0-31
> > NUMA node1 CPU(s):   32-63
> > NUMA node2 CPU(s):   64-95
> > NUMA node3 CPU(s):   96-127
> >
> > john@ubuntu:~$ lspci | grep -i non
> > 81:00.0 Non-Volatile memory controller: Huawei Technologies Co., Ltd. Device
> > 0123 (rev 45)
> >
> > cat /sys/block/nvme0n1/device/device/numa_node
> > 2
> BTW, nvme driver doesn't apply the pci numa node, and I guess the
> following patch is needed:
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 11779be42186..3c5e10e8b0c2 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -4366,7 +4366,11 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
>   	ctrl->dev = dev;
>   	ctrl->ops = ops;
>   	ctrl->quirks = quirks;
> +#ifdef CONFIG_NUMA
> +	ctrl->numa_node = dev->numa_node;
> +#else
>   	ctrl->numa_node = NUMA_NO_NODE;
> +#endif

From a quick look at the code, is this then later set for the PCI 
device in nvme_pci_configure_admin_queue()?

>   	INIT_WORK(&ctrl->scan_work, nvme_scan_work);
>   	INIT_WORK(&ctrl->async_event_work, nvme_async_event_work);
>   	INIT_WORK(&ctrl->fw_act_work, nvme_fw_act_work);
>
> > [   52.968495] nvme 0000:81:00.0: Adding to iommu group 5
> > [   52.980484] nvme nvme0: pci function 0000:81:00.0
> > [   52.999881] nvme nvme0: 23/0/0 default/read/poll queues
> Looks you didn't enabling polling. In irq mode, it isn't strange
> to observe IOPS difference when running fio on different CPUs.

If you are still keen to investigate more, then can try either of these:

- add iommu.strict=0 to the cmdline

- use perf record+annotate to find the hotspot
  - For this you need to enable psuedo-NMI with 2x steps:
    CONFIG_ARM64_PSEUDO_NMI=y in defconfig
    Add irqchip.gicv3_pseudo_nmi=1

    See 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/Kconfig#n1745
    Your kernel log should show:
    [    0.000000] GICv3: Pseudo-NMIs enabled using forced ICC_PMR_EL1 
synchronisation

But my impression is that this may be a HW implementation issue, 
considering we don't see such a huge drop off on our HW.

Thanks,
John