Re: [PATCH] virtio_vdpa: build affinity masks conditionally

[Michael S. Tsirkin]

On Fri, Aug 11, 2023 at 05:15:39AM -0400, Jason Wang wrote:
> We try to build affinity mask via create_affinity_masks()
> unconditionally which may lead several issues:
> 
> - the affinity mask is not used for parent without affinity support
>   (only VDUSE support the affinity now)
> - the logic of create_affinity_masks() might not work for devices
>   other than block. For example it's not rare in the networking device
>   where the number of queues could exceed the number of CPUs. Such
>   case breaks the current affinity logic which is based on
>   group_cpus_evenly() who assumes the number of CPUs are not less than
>   the number of groups. This can trigger a warning[1]:
> 
> 	if (ret >= 0)
> 		WARN_ON(nr_present + nr_others < numgrps);
> 
> Fixing this by only build the affinity masks only when
> 
> - Driver passes affinity descriptor, driver like virtio-blk can make
>   sure to limit the number of queues when it exceeds the number of CPUs
> - Parent support affinity setting config ops
> 
> This help to avoid the warning. More optimizations could be done on
> top.
> 
> [1]
> [  682.146655] WARNING: CPU: 6 PID: 1550 at lib/group_cpus.c:400 group_cpus_evenly+0x1aa/0x1c0
> [  682.146668] CPU: 6 PID: 1550 Comm: vdpa Not tainted 6.5.0-rc5jason+ #79
> [  682.146671] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014
> [  682.146673] RIP: 0010:group_cpus_evenly+0x1aa/0x1c0
> [  682.146676] Code: 4c 89 e0 5b 5d 41 5c 41 5d 41 5e c3 cc cc cc cc e8 1b c4 74 ff 48 89 ef e8 13 ac 98 ff 4c 89 e7 45 31 e4 e8 08 ac 98 ff eb c2 <0f> 0b eb b6 e8 fd 05 c3 00 45 31 e4 eb e5 cc cc cc cc cc cc cc cc
> [  682.146679] RSP: 0018:ffffc9000215f498 EFLAGS: 00010293
> [  682.146682] RAX: 000000000001f1e0 RBX: 0000000000000041 RCX: 0000000000000000
> [  682.146684] RDX: ffff888109922058 RSI: 0000000000000041 RDI: 0000000000000030
> [  682.146686] RBP: ffff888109922058 R08: ffffc9000215f498 R09: ffffc9000215f4a0
> [  682.146687] R10: 00000000000198d0 R11: 0000000000000030 R12: ffff888107e02800
> [  682.146689] R13: 0000000000000030 R14: 0000000000000030 R15: 0000000000000041
> [  682.146692] FS:  00007fef52315740(0000) GS:ffff888237380000(0000) knlGS:0000000000000000
> [  682.146695] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  682.146696] CR2: 00007fef52509000 CR3: 0000000110dbc004 CR4: 0000000000370ee0
> [  682.146698] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  682.146700] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [  682.146701] Call Trace:
> [  682.146703]  <TASK>
> [  682.146705]  ? __warn+0x7b/0x130
> [  682.146709]  ? group_cpus_evenly+0x1aa/0x1c0
> [  682.146712]  ? report_bug+0x1c8/0x1e0
> [  682.146717]  ? handle_bug+0x3c/0x70
> [  682.146721]  ? exc_invalid_op+0x14/0x70
> [  682.146723]  ? asm_exc_invalid_op+0x16/0x20
> [  682.146727]  ? group_cpus_evenly+0x1aa/0x1c0
> [  682.146729]  ? group_cpus_evenly+0x15c/0x1c0
> [  682.146731]  create_affinity_masks+0xaf/0x1a0
> [  682.146735]  virtio_vdpa_find_vqs+0x83/0x1d0
> [  682.146738]  ? __pfx_default_calc_sets+0x10/0x10
> [  682.146742]  virtnet_find_vqs+0x1f0/0x370
> [  682.146747]  virtnet_probe+0x501/0xcd0
> [  682.146749]  ? vp_modern_get_status+0x12/0x20
> [  682.146751]  ? get_cap_addr.isra.0+0x10/0xc0
> [  682.146754]  virtio_dev_probe+0x1af/0x260
> [  682.146759]  really_probe+0x1a5/0x410
> 
> Fixes: 3dad56823b53 ("virtio-vdpa: Support interrupt affinity spreading mechanism")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>

This won't fix the case where block has more queues than CPUs though,
will it?

> ---
>  drivers/virtio/virtio_vdpa.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> index 961161da5900..06ce6d8c2e00 100644
> --- a/drivers/virtio/virtio_vdpa.c
> +++ b/drivers/virtio/virtio_vdpa.c
> @@ -366,11 +366,14 @@ static int virtio_vdpa_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
>  	struct irq_affinity default_affd = { 0 };
>  	struct cpumask *masks;
>  	struct vdpa_callback cb;
> +	bool has_affinity = desc && ops->set_vq_affinity;
>  	int i, err, queue_idx = 0;
>  
> -	masks = create_affinity_masks(nvqs, desc ? desc : &default_affd);
> -	if (!masks)
> -		return -ENOMEM;
> +	if (has_affinity) {
> +		masks = create_affinity_masks(nvqs, desc ? desc : &default_affd);
> +		if (!masks)
> +			return -ENOMEM;
> +	}
>  
>  	for (i = 0; i < nvqs; ++i) {
>  		if (!names[i]) {
> @@ -386,20 +389,22 @@ static int virtio_vdpa_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
>  			goto err_setup_vq;
>  		}
>  
> -		if (ops->set_vq_affinity)
> +		if (has_affinity)
>  			ops->set_vq_affinity(vdpa, i, &masks[i]);
>  	}
>  
>  	cb.callback = virtio_vdpa_config_cb;
>  	cb.private = vd_dev;
>  	ops->set_config_cb(vdpa, &cb);
> -	kfree(masks);
> +	if (has_affinity)
> +		kfree(masks);
>  
>  	return 0;
>  
>  err_setup_vq:
>  	virtio_vdpa_del_vqs(vdev);
> -	kfree(masks);
> +	if (has_affinity)
> +		kfree(masks);
>  	return err;
>  }
>  
> -- 
> 2.39.3