On Thu, Feb 18, 2021 at 01:39:19PM +0800, Jason Wang wrote: > > On 2021/2/10 下午5:14, Michael S. Tsirkin wrote: > > On Tue, Feb 09, 2021 at 10:00:22AM -0800, Wei Wang wrote: > > > On Tue, Feb 9, 2021 at 6:58 AM Willem de Bruijn > > > <willemdebruijn.kernel@xxxxxxxxx> wrote: > > > > > > > > I have no preference. Just curious, especially if it complicates the patch. > > > > > > > > > > > > > > > My understanding is that. It's probably ok for net. But we probably need > > > > > > > to document the assumptions to make sure it was not abused in other drivers. > > > > > > > > > > > > > > Introduce new parameters for find_vqs() can help to eliminate the subtle > > > > > > > stuffs but I agree it looks like a overkill. > > > > > > > > > > > > > > (Btw, I forget the numbers but wonder how much difference if we simple > > > > > > > remove the free_old_xmits() from the rx NAPI path?) > > > > > > The committed patchset did not record those numbers, but I found them > > > > > > in an earlier iteration: > > > > > > > > > > > > [PATCH net-next 0/3] virtio-net tx napi > > > > > > https://lists.openwall.net/netdev/2017/04/02/55 > > > > > > > > > > > > It did seem to significantly reduce compute cycles ("Gcyc") at the > > > > > > time. For instance: > > > > > > > > > > > > TCP_RR Latency (us): > > > > > > 1x: > > > > > > p50 24 24 21 > > > > > > p99 27 27 27 > > > > > > Gcycles 299 432 308 > > > > > > > > > > > > I'm concerned that removing it now may cause a regression report in a > > > > > > few months. That is higher risk than the spurious interrupt warning > > > > > > that was only reported after years of use. > > > > > > > > > > Right. > > > > > > > > > > So if Michael is fine with this approach, I'm ok with it. But we > > > > > probably need to a TODO to invent the interrupt handlers that can be > > > > > used for more than one virtqueues. When MSI-X is enabled, the interrupt > > > > > handler (vring_interrup()) assumes the interrupt is used by a single > > > > > virtqueue. > > > > Thanks. > > > > > > > > The approach to schedule tx-napi from virtnet_poll_cleantx instead of > > > > cleaning directly in this rx-napi function was not effective at > > > > suppressing the warning, I understand. > > > Correct. I tried the approach to schedule tx napi instead of directly > > > do free_old_xmit_skbs() in virtnet_poll_cleantx(). But the warning > > > still happens. > > Two questions here: is the device using packed or split vqs? > > And is event index enabled? > > > > I think one issue is that at the moment with split and event index we > > don't actually disable events at all. > > > Do we really have a way to disable that? (We don't have a flag like packed > virtqueue) > > Or you mean the trick [1] when I post tx interrupt RFC? > > Thanks > > [1] https://lkml.org/lkml/2015/2/9/113 Something like this. Or basically any other value will do, e.g. move the index back to a value just signalled ... > > > > > static void virtqueue_disable_cb_split(struct virtqueue *_vq) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { > > vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; > > if (!vq->event) > > vq->split.vring.avail->flags = > > cpu_to_virtio16(_vq->vdev, > > vq->split.avail_flags_shadow); > > } > > } > > > > Can you try your napi patch + disable event index? > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
