On Mon, Jul 24, 2023 at 3:17 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Mon, Jul 24, 2023 at 02:52:05PM +0800, Jason Wang wrote: > > On Sat, Jul 22, 2023 at 4:18 AM Maxime Coquelin > > <maxime.coquelin@xxxxxxxxxx> wrote: > > > > > > > > > > > > On 7/21/23 17:10, Michael S. Tsirkin wrote: > > > > On Fri, Jul 21, 2023 at 04:58:04PM +0200, Maxime Coquelin wrote: > > > >> > > > >> > > > >> On 7/21/23 16:45, Michael S. Tsirkin wrote: > > > >>> On Fri, Jul 21, 2023 at 04:37:00PM +0200, Maxime Coquelin wrote: > > > >>>> > > > >>>> > > > >>>> On 7/20/23 23:02, Michael S. Tsirkin wrote: > > > >>>>> On Thu, Jul 20, 2023 at 01:26:20PM -0700, Shannon Nelson wrote: > > > >>>>>> On 7/20/23 1:38 AM, Jason Wang wrote: > > > >>>>>>> > > > >>>>>>> Adding cond_resched() to the command waiting loop for a better > > > >>>>>>> co-operation with the scheduler. This allows to give CPU a breath to > > > >>>>>>> run other task(workqueue) instead of busy looping when preemption is > > > >>>>>>> not allowed on a device whose CVQ might be slow. > > > >>>>>>> > > > >>>>>>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > > >>>>>> > > > >>>>>> This still leaves hung processes, but at least it doesn't pin the CPU any > > > >>>>>> more. Thanks. > > > >>>>>> Reviewed-by: Shannon Nelson <shannon.nelson@xxxxxxx> > > > >>>>>> > > > >>>>> > > > >>>>> I'd like to see a full solution > > > >>>>> 1- block until interrupt > > > > I remember in previous versions, you worried about the extra MSI > > vector. (Maybe I was wrong). > > > > > >>>> > > > >>>> Would it make sense to also have a timeout? > > > >>>> And when timeout expires, set FAILED bit in device status? > > > >>> > > > >>> virtio spec does not set any limits on the timing of vq > > > >>> processing. > > > >> > > > >> Indeed, but I thought the driver could decide it is too long for it. > > > >> > > > >> The issue is we keep waiting with rtnl locked, it can quickly make the > > > >> system unusable. > > > > > > > > if this is a problem we should find a way not to keep rtnl > > > > locked indefinitely. > > > > Any ideas on this direction? Simply dropping rtnl during the busy loop > > will result in a lot of races. This seems to require non-trivial > > changes in the networking core. > > > > > > > > From the tests I have done, I think it is. With OVS, a reconfiguration > > > is performed when the VDUSE device is added, and when a MLX5 device is > > > in the same bridge, it ends up doing an ioctl() that tries to take the > > > rtnl lock. In this configuration, it is not possible to kill OVS because > > > it is stuck trying to acquire rtnl lock for mlx5 that is held by virtio- > > > net. > > > > Yeah, basically, any RTNL users would be blocked forever. > > > > And the infinite loop has other side effects like it blocks the freezer to work. > > > > To summarize, there are three issues > > > > 1) busy polling > > 2) breaks freezer > > 3) hold RTNL during the loop > > > > Solving 3 may help somehow for 2 e.g some pm routine e.g wireguard or > > even virtnet_restore() itself may try to hold the lock. > > Yep. So my feeling currently is, the only real fix is to actually > queue up the work in software. Do you mean something like: rtnl_lock(); queue up the work rtnl_unlock(); return success; ? > It's mostly trivial to limit > memory consumption, vid's is the > only one where it would make sense to have more than > 1 command of a given type outstanding. And rx mode so this implies we will fail any command if the previous work is not finished. > have a tree > or a bitmap with vids to add/remove? Probably. Thanks > > > > > > > > > > > > > >>>>> 2- still handle surprise removal correctly by waking in that case > > > > This is basically what version 1 did? > > > > https://lore.kernel.org/lkml/6026e801-6fda-fee9-a69b-d06a80368621@xxxxxxxxxx/t/ > > > > Thanks > > Yes - except the timeout part. > > > > > >>>>> > > > >>>>> > > > >>>>> > > > >>>>>>> --- > > > >>>>>>> drivers/net/virtio_net.c | 4 +++- > > > >>>>>>> 1 file changed, 3 insertions(+), 1 deletion(-) > > > >>>>>>> > > > >>>>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > >>>>>>> index 9f3b1d6ac33d..e7533f29b219 100644 > > > >>>>>>> --- a/drivers/net/virtio_net.c > > > >>>>>>> +++ b/drivers/net/virtio_net.c > > > >>>>>>> @@ -2314,8 +2314,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd, > > > >>>>>>> * into the hypervisor, so the request should be handled immediately. > > > >>>>>>> */ > > > >>>>>>> while (!virtqueue_get_buf(vi->cvq, &tmp) && > > > >>>>>>> - !virtqueue_is_broken(vi->cvq)) > > > >>>>>>> + !virtqueue_is_broken(vi->cvq)) { > > > >>>>>>> + cond_resched(); > > > >>>>>>> cpu_relax(); > > > >>>>>>> + } > > > >>>>>>> > > > >>>>>>> return vi->ctrl->status == VIRTIO_NET_OK; > > > >>>>>>> } > > > >>>>>>> -- > > > >>>>>>> 2.39.3 > > > >>>>>>> > > > >>>>>>> _______________________________________________ > > > >>>>>>> Virtualization mailing list > > > >>>>>>> Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx > > > >>>>>>> https://lists.linuxfoundation.org/mailman/listinfo/virtualization > > > >>>>> > > > >>> > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
