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Message-ID: <CAHS8izOosrkGw_aaL4-Rf1ue8UOMvaWWYXc48OBjO4F2UQa3VQ@mail.gmail.com>
Date: Mon, 18 Aug 2025 11:24:16 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: asml.silence@...il.com, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>, cratiu@...dia.com, tariqt@...dia.com, parav@...dia.com,
Christoph Hellwig <hch@...radead.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next v3 6/7] net: devmem: pre-read requested rx queues
during bind
On Sat, Aug 16, 2025 at 1:59 AM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> On Fri, Aug 15, 2025 at 11:05:56AM -0700, Mina Almasry wrote:
> > On Fri, Aug 15, 2025 at 4:07 AM Dragos Tatulea <dtatulea@...dia.com> wrote:
> > >
> > > Instead of reading the requested rx queues after binding the buffer,
> > > read the rx queues in advance in a bitmap and iterate over them when
> > > needed.
> > >
> > > This is a preparation for fetching the DMA device for each queue.
> > >
> > > This patch has no functional changes.
> > >
> > > Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> > > ---
> > > net/core/netdev-genl.c | 76 +++++++++++++++++++++++++++---------------
> > > 1 file changed, 49 insertions(+), 27 deletions(-)
> > >
> > > diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> > > index 3e2d6aa6e060..3e990f100bf0 100644
> > > --- a/net/core/netdev-genl.c
> > > +++ b/net/core/netdev-genl.c
> > > @@ -869,17 +869,50 @@ int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
> > > return err;
> > > }
> > >
> > > -int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> > > +static int netdev_nl_read_rxq_bitmap(struct genl_info *info,
> > > + unsigned long *rxq_bitmap)
> > > {
> > > struct nlattr *tb[ARRAY_SIZE(netdev_queue_id_nl_policy)];
> > > + struct nlattr *attr;
> > > + int rem, err = 0;
> > > + u32 rxq_idx;
> > > +
> > > + nla_for_each_attr_type(attr, NETDEV_A_DMABUF_QUEUES,
> > > + genlmsg_data(info->genlhdr),
> > > + genlmsg_len(info->genlhdr), rem) {
> > > + err = nla_parse_nested(
> > > + tb, ARRAY_SIZE(netdev_queue_id_nl_policy) - 1, attr,
> > > + netdev_queue_id_nl_policy, info->extack);
> > > + if (err < 0)
> > > + return err;
> > > +
> > > + if (NL_REQ_ATTR_CHECK(info->extack, attr, tb, NETDEV_A_QUEUE_ID) ||
> > > + NL_REQ_ATTR_CHECK(info->extack, attr, tb, NETDEV_A_QUEUE_TYPE))
> > > + return -EINVAL;
> > > +
> > > + if (nla_get_u32(tb[NETDEV_A_QUEUE_TYPE]) != NETDEV_QUEUE_TYPE_RX) {
> > > + NL_SET_BAD_ATTR(info->extack, tb[NETDEV_A_QUEUE_TYPE]);
> > > + return -EINVAL;
> > > + }
> > > +
> > > + rxq_idx = nla_get_u32(tb[NETDEV_A_QUEUE_ID]);
> > > +
> > > + bitmap_set(rxq_bitmap, rxq_idx, 1);
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> > > +{
> > > struct net_devmem_dmabuf_binding *binding;
> > > u32 ifindex, dmabuf_fd, rxq_idx;
> > > struct netdev_nl_sock *priv;
> > > struct net_device *netdev;
> > > + unsigned long *rxq_bitmap;
> > > struct device *dma_dev;
> > > struct sk_buff *rsp;
> > > - struct nlattr *attr;
> > > - int rem, err = 0;
> > > + int err = 0;
> > > void *hdr;
> > >
> > > if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX) ||
> > > @@ -922,37 +955,22 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> > > goto err_unlock;
> > > }
> > >
> > > + rxq_bitmap = bitmap_alloc(netdev->num_rx_queues, GFP_KERNEL);
> > > + if (!rxq_bitmap) {
> > > + err = -ENOMEM;
> > > + goto err_unlock;
> > > + }
> > > + netdev_nl_read_rxq_bitmap(info, rxq_bitmap);
> > > +
> > > dma_dev = netdev_queue_get_dma_dev(netdev, 0);
> > > binding = net_devmem_bind_dmabuf(netdev, dma_dev, DMA_FROM_DEVICE,
> > > dmabuf_fd, priv, info->extack);
> > > if (IS_ERR(binding)) {
> > > err = PTR_ERR(binding);
> > > - goto err_unlock;
> > > + goto err_rxq_bitmap;
> > > }
> > >
> > > - nla_for_each_attr_type(attr, NETDEV_A_DMABUF_QUEUES,
> > > - genlmsg_data(info->genlhdr),
> > > - genlmsg_len(info->genlhdr), rem) {
> > > - err = nla_parse_nested(
> > > - tb, ARRAY_SIZE(netdev_queue_id_nl_policy) - 1, attr,
> > > - netdev_queue_id_nl_policy, info->extack);
> > > - if (err < 0)
> > > - goto err_unbind;
> > > -
> > > - if (NL_REQ_ATTR_CHECK(info->extack, attr, tb, NETDEV_A_QUEUE_ID) ||
> > > - NL_REQ_ATTR_CHECK(info->extack, attr, tb, NETDEV_A_QUEUE_TYPE)) {
> > > - err = -EINVAL;
> > > - goto err_unbind;
> > > - }
> > > -
> > > - if (nla_get_u32(tb[NETDEV_A_QUEUE_TYPE]) != NETDEV_QUEUE_TYPE_RX) {
> > > - NL_SET_BAD_ATTR(info->extack, tb[NETDEV_A_QUEUE_TYPE]);
> > > - err = -EINVAL;
> > > - goto err_unbind;
> > > - }
> > > -
> > > - rxq_idx = nla_get_u32(tb[NETDEV_A_QUEUE_ID]);
> > > -
> > > + for_each_set_bit(rxq_idx, rxq_bitmap, netdev->num_rx_queues) {
> >
> > Is this code assuming that netdev->num_rx_queues (or
> > real_num_rx_queues) <= BITS_PER_ULONG? Aren't there devices out there
> > that support more than 64 hardware queues? If so, I guess you need a
> > different data structure than a bitmap (or maybe there is arbirary
> > sized bitmap library somewhere to use).
> >
> The bitmap API can handle any number of bits. Can it not?
>
Ah, yes, I missed this:
+ rxq_bitmap = bitmap_alloc(netdev->num_rx_queues, GFP_KERNEL);
Which allocates netdev->num_rx_queues bits. I was confused by the fact
that rxq_bitmap is an unsigned long * and thought that was the # of
bits in the map.
This patch should be good just with conversion to netdev->real_num_rx_queues.
--
Thanks,
Mina
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