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From:   Jason Wang <jasowang@redhat.com>
Date:   Fri, 11 Aug 2023 17:41:44 +0800
Message-ID: <CACGkMEuO+smLSY+dRvDOar=pq6MpOv3U9z6gX=xRUkHg494MFw@mail.gmail.com>
Subject: Re: [PATCH] virtio_vdpa: build affinity masks conditionally
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     xuanzhuo@linux.alibaba.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, xieyongji@bytedance.com
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On Fri, Aug 11, 2023 at 5:25=E2=80=AFPM Michael S. Tsirkin <mst@redhat.com>=
 wrote:
>
> 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 >=3D 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), B=
IOS 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: 0000000=
000000000
> > [  682.146684] RDX: ffff888109922058 RSI: 0000000000000041 RDI: 0000000=
000000030
> > [  682.146686] RBP: ffff888109922058 R08: ffffc9000215f498 R09: ffffc90=
00215f4a0
> > [  682.146687] R10: 00000000000198d0 R11: 0000000000000030 R12: ffff888=
107e02800
> > [  682.146689] R13: 0000000000000030 R14: 0000000000000030 R15: 0000000=
000000041
> > [  682.146692] FS:  00007fef52315740(0000) GS:ffff888237380000(0000) kn=
lGS:0000000000000000
> > [  682.146695] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [  682.146696] CR2: 00007fef52509000 CR3: 0000000110dbc004 CR4: 0000000=
000370ee0
> > [  682.146698] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000=
000000000
> > [  682.146700] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000=
000000400
> > [  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@redhat.com>
>
> This won't fix the case where block has more queues than CPUs though,
> will it?

Block will limit the number of queues during init_vq():

        num_vqs =3D min_t(unsigned int,
                        min_not_zero(num_request_queues, nr_cpu_ids),
                        num_vqs);


Thanks

>
> > ---
> >  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_dev=
ice *vdev, unsigned int nvqs,
> >       struct irq_affinity default_affd =3D { 0 };
> >       struct cpumask *masks;
> >       struct vdpa_callback cb;
> > +     bool has_affinity =3D desc && ops->set_vq_affinity;
> >       int i, err, queue_idx =3D 0;
> >
> > -     masks =3D create_affinity_masks(nvqs, desc ? desc : &default_affd=
);
> > -     if (!masks)
> > -             return -ENOMEM;
> > +     if (has_affinity) {
> > +             masks =3D create_affinity_masks(nvqs, desc ? desc : &defa=
ult_affd);
> > +             if (!masks)
> > +                     return -ENOMEM;
> > +     }
> >
> >       for (i =3D 0; i < nvqs; ++i) {
> >               if (!names[i]) {
> > @@ -386,20 +389,22 @@ static int virtio_vdpa_find_vqs(struct virtio_dev=
ice *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 =3D virtio_vdpa_config_cb;
> >       cb.private =3D 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
>