Re: [PATCH] block/mq: blk map queues by core id

From: Dongli Zhang
Date: Mon Mar 25 2019 - 09:53:26 EST

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On 03/25/2019 05:53 PM, luferry wrote:
>
> sorry, messed up some func name
>
> When enable virtio-blk with multi queues but with only 2 msix-vector.
> vp_dev->per_vq_vectors will be false, so blk_mq_virtio_map_queues will fallback to blk_mq_map_queues
>
> Since virtual machine users cannot change the vector numbers, I think blk_mq_map_queues should be more friendly with different cpu topology.

Yes, we will fallback to blk_mq_map_queues if there is lack of vectors.

Here is the qemu cmdline:
"-smp 8,sockets=1,cores=4,threads=2"
"-device virtio-blk-pci,drive=drive0,id=device0,num-queues=4,vectors=2"

# cat /sys/block/vda/mq/0/cpu_list
0, 4, 5
root@vm:/home/zhang# cat /sys/block/vda/mq/1/cpu_list
1
root@vm:/home/zhang# cat /sys/block/vda/mq/2/cpu_list
2, 6, 7
root@vm:/home/zhang# cat /sys/block/vda/mq/3/cpu_list
3

How about to put how to hit the issue in commit message so people would be able
to know the scenario?

Dongli Zhang

>
>
>
>
> At 2019-03-25 17:49:33, "luferry" <luferry@xxxxxxx> wrote:
>>
>> After reading the code and compare pci device info.
>> I can reproduce this imbalance under KVM.
>> When enable virtio-blk with multi queues but with only 2 msix-vector.
>> vp_dev->per_vq_vectors will be false, so blk_mq_virtio_map_queues will fallback to virtio_mq_map_queues
>>
>> Since virtual machine users cannot change the vector numbers, I think virtio_mq_map_queues should be more friendly with different cpu topology.
>>
>> 448 const struct cpumask *vp_get_vq_affinity(struct virtio_device *vdev, int index)
>> 449 {
>> 450 struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>> 451
>> 452 if (!vp_dev->per_vq_vectors ||
>> 453 vp_dev->vqs[index]->msix_vector == VIRTIO_MSI_NO_VECTOR)
>> 454 return NULL;
>> 455
>> 456 return pci_irq_get_affinity(vp_dev->pci_dev,
>> 457 vp_dev->vqs[index]->msix_vector);
>> 458 }
>>
>> 32 int blk_mq_virtio_map_queues(struct blk_mq_queue_map *qmap,
>> 33 struct virtio_device *vdev, int first_vec)
>> 34 {
>> 35 const struct cpumask *mask;
>> 36 unsigned int queue, cpu;
>> 37
>> 38 if (!vdev->config->get_vq_affinity)
>> 39 goto fallback;
>> 40
>> 41 for (queue = 0; queue < qmap->nr_queues; queue++) {
>> 42 mask = vdev->config->get_vq_affinity(vdev, first_vec + queue); //vp_get_vq_affinity
>> 43 if (!mask)
>> 44 goto fallback;
>> 45
>> 46 for_each_cpu(cpu, mask)
>> 47 qmap->mq_map[cpu] = qmap->queue_offset + queue;
>> 48 }
>> 49
>> 50 return 0;
>> 51 fallback:
>> 52 return blk_mq_map_queues(qmap);
>> 53 }
>>
>>
>>
>>
>>
>>
>>
>>
>> At 2019-03-23 19:14:34, "Dongli Zhang" <dongli.zhang@xxxxxxxxxx> wrote:
>>>
>>>
>>> On 03/23/2019 02:34 PM, luferry wrote:
>>>>
>>>> I just bought one vm , so i cannot access to hypervisor. I will try to build the environment on my desktop.
>>>> I'm sure about something.
>>>> The hypervisor is KVM and disk driver is virtio-blk.
>>>> [root@blk-mq ~]# dmesg |grep KVM
>>>> [ 0.000000] Hypervisor detected: KVM
>>>> [ 0.186330] Booting paravirtualized kernel on KVM
>>>> [ 0.279106] KVM setup async PF for cpu 0
>>>> [ 0.420819] KVM setup async PF for cpu 1
>>>> [ 0.421682] KVM setup async PF for cpu 2
>>>> [ 0.422113] KVM setup async PF for cpu 3
>>>> [ 0.422434] KVM setup async PF for cpu 4
>>>> [ 0.422434] KVM setup async PF for cpu 5
>>>> [ 0.423312] KVM setup async PF for cpu 6
>>>> [ 0.423394] KVM setup async PF for cpu 7
>>>> [ 0.424125] KVM setup async PF for cpu 8
>>>> [ 0.424414] KVM setup async PF for cpu 9
>>>> [ 0.424415] KVM setup async PF for cpu 10
>>>> [ 0.425329] KVM setup async PF for cpu 11
>>>> [ 0.425420] KVM setup async PF for cpu 12
>>>> [ 0.426156] KVM setup async PF for cpu 13
>>>> [ 0.426431] KVM setup async PF for cpu 14
>>>> [ 0.426431] KVM setup async PF for cpu 15
>>>> [root@blk-mq ~]# lspci |grep block
>>>> 00:05.0 SCSI storage controller: Red Hat, Inc. Virtio block device
>>>> 00:06.0 SCSI storage controller: Red Hat, Inc. Virtio block device
>>>>
>>>> [root@blk-mq ~]# lscpu
>>>> Architecture: x86_64
>>>> CPU op-mode(s): 32-bit, 64-bit
>>>> Byte Order: Little Endian
>>>> CPU(s): 16
>>>> On-line CPU(s) list: 0-15
>>>> Thread(s) per core: 2
>>>> Core(s) per socket: 8
>>>>
>>>> [root@blk-mq ~]# ls /sys/block/vdb/mq/
>>>> 0 1 2 3
>>>>
>>>> [root@blk-mq ~]# cat /proc/cpuinfo |egrep 'processor|core id'
>>>> processor : 0
>>>> core id : 0
>>>> processor : 1
>>>> core id : 0
>>>> processor : 2
>>>> core id : 1
>>>> processor : 3
>>>> core id : 1
>>>> processor : 4
>>>> core id : 2
>>>> processor : 5
>>>> core id : 2
>>>> processor : 6
>>>> core id : 3
>>>> processor : 7
>>>> core id : 3
>>>> processor : 8
>>>> core id : 4
>>>> processor : 9
>>>> core id : 4
>>>> processor : 10
>>>> core id : 5
>>>> processor : 11
>>>> core id : 5
>>>> processor : 12
>>>> core id : 6
>>>> processor : 13
>>>> core id : 6
>>>> processor : 14
>>>> core id : 7
>>>> processor : 15
>>>> core id : 7
>>>>
>>>> --before this patch--
>>>> [root@blk-mq ~]# cat /sys/block/vdb/mq/*/cpu_list
>>>> 0, 4, 5, 8, 9, 12, 13
>>>> 1
>>>> 2, 6, 7, 10, 11, 14, 15
>>>> 3
>>>>
>>>> --after this patch--
>>>> [root@blk-mq ~]# cat /sys/block/vdb/mq/*/cpu_list
>>>> 0, 4, 5, 12, 13
>>>> 1, 6, 7, 14, 15
>>>> 2, 8, 9
>>>> 3, 10, 11
>>>>
>>>>
>>>> I add dump_stack insert blk_mq_map_queues.
>>>>
>>>> [ 1.378680] Call Trace:
>>>> [ 1.378690] dump_stack+0x5a/0x73
>>>> [ 1.378695] blk_mq_map_queues+0x29/0xb0
>>>> [ 1.378700] blk_mq_alloc_tag_set+0x1bd/0x2d0
>>>> [ 1.378705] virtblk_probe+0x1ae/0x8e4 [virtio_blk]
>>>> [ 1.378709] virtio_dev_probe+0x18a/0x230 [virtio]
>>>> [ 1.378713] really_probe+0x215/0x3f0
>>>> [ 1.378716] driver_probe_device+0x115/0x130
>>>> [ 1.378718] device_driver_attach+0x50/0x60
>>>> [ 1.378720] __driver_attach+0xbd/0x140
>>>> [ 1.378722] ? device_driver_attach+0x60/0x60
>>>> [ 1.378724] bus_for_each_dev+0x67/0xc0
>>>> [ 1.378727] ? klist_add_tail+0x57/0x70
>>>
>>> I am not able to reproduce above call stack when virtio-blk is assigned 4 queues
>>> while my qemu cmdline is "-smp 16,sockets=1,cores=8,threads=2".
>>>
>>> # cat /sys/block/vda/mq/0/cpu_list
>>> 0, 1, 2, 3
>>> # cat /sys/block/vda/mq/1/cpu_list
>>> 4, 5, 6, 7
>>> # cat /sys/block/vda/mq/2/cpu_list
>>> 8, 9, 10, 11
>>> # cat /sys/block/vda/mq/3/cpu_list
>>> 12, 13, 14, 15
>>>
>>>
>>> I do agree in above case we would have issue if the mapping is established by
>>> blk_mq_map_queues().
>>>
>>>
>>> However, I am just curious how we finally reach at blk_mq_map_queues() from
>>> blk_mq_alloc_tag_set()?
>>>
>>> It should be something like:
>>>
>>> blk_mq_alloc_tag_set()
>>> -> blk_mq_update_queue_map()
>>> -> if (set->ops->map_queues && !is_kdump_kernel())
>>> return set->ops->map_queues(set);
>>> -> else
>>> return blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
>>>
>>> Wouldn't we always have set->ops->map_queues = virtblk_map_queues()?
>>>
>>> Or the execution reach at:
>>>
>>> virtblk_map_queues()
>>> -> blk_mq_virtio_map_queues()
>>> -> if (!vdev->config->get_vq_affinity)
>>> return blk_mq_map_queues(qmap);
>>> -> else
>>> establish the mapping via get_vq_affinity
>>>
>>> but vdev->config->get_vq_affinity == NULL?
>>>
>>> For virtio pci, get_vq_affinity is always set. Seems virtio mmio would not set
>>> get_vq_affinity.
>>>
>>>
>>> I used to play with firecracker (by amazon) and it is interesting firecracker
>>> uses mmio to setup virtio-blk.
>>>
>>>
>>> Sorry for disturbing the review of this patch. I just would like to clarify in
>>> which scenario we would hit this issue, e.g., when virtio-blk is based on mmio?
>>>
>>> Dongli Zhang
>>>
>>>>
>>>>
>>>> At 2019-03-22 19:58:08, "Dongli Zhang" <dongli.zhang@xxxxxxxxxx> wrote:
>>>>>
>>>>>
>>>>> On 03/22/2019 06:09 PM, luferry wrote:
>>>>>> under virtual machine environment, cpu topology may differ from normal
>>>>>> physical server.
>>>>>
>>>>> Would mind share the name of virtual machine monitor, the command line if
>>>>> available, and which device to reproduce.
>>>>>
>>>>> For instance, I am not able to reproduce with qemu nvme or virtio-blk as I
>>>>> assume they use pci or virtio specific mapper to establish the mapping.
>>>>>
>>>>> E.g., with qemu and nvme: -smp 8,sockets=1,cores=4,threads=2
>>>>>
>>>>> Indeed I use three queues instead of twp as one is reserved for admin.
>>>>>
>>>>> # ls /sys/block/nvme0n1/mq/*
>>>>> /sys/block/nvme0n1/mq/0:
>>>>> cpu0 cpu1 cpu2 cpu3 cpu_list nr_reserved_tags nr_tags
>>>>>
>>>>> /sys/block/nvme0n1/mq/1:
>>>>> cpu4 cpu5 cpu6 cpu7 cpu_list nr_reserved_tags nr_tags
>>>>>
>>>>>
>>>>> Thank you very much!
>>>>>
>>>>> Dongli Zhang
>>>>>
>>>>>> for example (machine with 4 cores, 2 threads per core):
>>>>>>
>>>>>> normal physical server:
>>>>>> core-id thread-0-id thread-1-id
>>>>>> 0 0 4
>>>>>> 1 1 5
>>>>>> 2 2 6
>>>>>> 3 3 7
>>>>>>
>>>>>> virtual machine:
>>>>>> core-id thread-0-id thread-1-id
>>>>>> 0 0 1
>>>>>> 1 2 3
>>>>>> 2 4 5
>>>>>> 3 6 7
>>>>>>
>>>>>> When attach disk with two queues, all the even numbered cpus will be
>>>>>> mapped to queue 0. Under virtual machine, all the cpus is followed by
>>>>>> its sibling cpu.Before this patch, all the odd numbered cpus will also
>>>>>> be mapped to queue 0, can cause serious imbalance.this will lead to
>>>>>> performance impact on system IO
>>>>>>
>>>>>> So suggest to allocate cpu map by core id, this can be more currency
>>>>>>
>>>>>> Signed-off-by: luferry <luferry@xxxxxxx>
>>>>>> ---
>>>>>> block/blk-mq-cpumap.c | 9 +++++----
>>>>>> 1 file changed, 5 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
>>>>>> index 03a534820271..4125e8e77679 100644
>>>>>> --- a/block/blk-mq-cpumap.c
>>>>>> +++ b/block/blk-mq-cpumap.c
>>>>>> @@ -35,7 +35,7 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
>>>>>> {
>>>>>> unsigned int *map = qmap->mq_map;
>>>>>> unsigned int nr_queues = qmap->nr_queues;
>>>>>> - unsigned int cpu, first_sibling;
>>>>>> + unsigned int cpu, first_sibling, core = 0;
>>>>>>
>>>>>> for_each_possible_cpu(cpu) {
>>>>>> /*
>>>>>> @@ -48,9 +48,10 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
>>>>>> map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
>>>>>> } else {
>>>>>> first_sibling = get_first_sibling(cpu);
>>>>>> - if (first_sibling == cpu)
>>>>>> - map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
>>>>>> - else
>>>>>> + if (first_sibling == cpu) {
>>>>>> + map[cpu] = cpu_to_queue_index(qmap, nr_queues, core);
>>>>>> + core++;
>>>>>> + } else
>>>>>> map[cpu] = map[first_sibling];
>>>>>> }
>>>>>> }
>>>>>>

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In reply to: luferry: "Re:Re:Re: [PATCH] block/mq: blk map queues by core id"
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