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

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


At 2019-03-22 19:58:08, "Dongli Zhang" <dongli.zhang@oracle.com> 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@163.com>
>> ---
>> 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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