Message-ID: <20210702111857.jfmeuxnkwg6v7krk@apollo>
Date:   Fri, 2 Jul 2021 16:48:57 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>, bpf@...r.kernel.org,
        Eric Leblond <eric@...it.org>
Subject: Re: [PATCH net-next v5 3/5] bpf: cpumap: implement generic cpumap

On Thu, Jul 01, 2021 at 02:46:05PM IST, Jesper Dangaard Brouer wrote:
> (Cc. Eric Leblond as he needed this for Suricata.)
>
> On 01/07/2021 02.27, Kumar Kartikeya Dwivedi wrote:
> > This change implements CPUMAP redirect support for generic XDP programs.
> > The idea is to reuse the cpu map entry's queue that is used to push
> > native xdp frames for redirecting skb to a different CPU. This will
> > match native XDP behavior (in that RPS is invoked again for packet
> > reinjected into networking stack).
> >
> > To be able to determine whether the incoming skb is from the driver or
> > cpumap, we reuse skb->redirected bit that skips generic XDP processing
> > when it is set. To always make use of this, CONFIG_NET_REDIRECT guard on
> > it has been lifted and it is always available.
> >
> >  From the redirect side, we add the skb to ptr_ring with its lowest bit
> > set to 1.  This should be safe as skb is not 1-byte aligned. This allows
> > kthread to discern between xdp_frames and sk_buff. On consumption of the
> > ptr_ring item, the lowest bit is unset.
> >
> > In the end, the skb is simply added to the list that kthread is anyway
> > going to maintain for xdp_frames converted to skb, and then received
> > again by using netif_receive_skb_list.
> >
> > Bulking optimization for generic cpumap is left as an exercise for a
> > future patch for now.
> Fine by me, I hope bulking is added later, as I think with bulking this will
> be a faster alternative than RPS.
> >
> > Since cpumap entry progs are now supported, also remove check in
> > generic_xdp_install for the cpumap.
> >
> > Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> > ---
> >   include/linux/bpf.h    |   9 +++-
> >   include/linux/skbuff.h |  10 +---
> >   kernel/bpf/cpumap.c    | 115 +++++++++++++++++++++++++++++++++++------
> >   net/core/dev.c         |   3 +-
> >   net/core/filter.c      |   6 ++-
> >   5 files changed, 115 insertions(+), 28 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index f309fc1509f2..095aaa104c56 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1513,7 +1513,8 @@ bool dev_map_can_have_prog(struct bpf_map *map);
> >   void __cpu_map_flush(void);
> >   int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp,
> >   		    struct net_device *dev_rx);
> > -bool cpu_map_prog_allowed(struct bpf_map *map);
> > +int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
> > +			     struct sk_buff *skb);
> >   /* Return map's numa specified by userspace */
> >   static inline int bpf_map_attr_numa_node(const union bpf_attr *attr)
> > @@ -1710,6 +1711,12 @@ static inline int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu,
> >   	return 0;
> >   }
> > +static inline int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
> > +					   struct sk_buff *skb)
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> > +
> >   static inline bool cpu_map_prog_allowed(struct bpf_map *map)
> >   {
> >   	return false;
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index b2db9cd9a73f..f19190820e63 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -863,8 +863,8 @@ struct sk_buff {
> >   	__u8			tc_skip_classify:1;
> >   	__u8			tc_at_ingress:1;
> >   #endif
> > -#ifdef CONFIG_NET_REDIRECT
> >   	__u8			redirected:1;
> > +#ifdef CONFIG_NET_REDIRECT
> >   	__u8			from_ingress:1;
> >   #endif
> >   #ifdef CONFIG_TLS_DEVICE
> > @@ -4664,17 +4664,13 @@ static inline __wsum lco_csum(struct sk_buff *skb)
> >   static inline bool skb_is_redirected(const struct sk_buff *skb)
> >   {
> > -#ifdef CONFIG_NET_REDIRECT
> >   	return skb->redirected;
> > -#else
> > -	return false;
> > -#endif
> >   }
> >   static inline void skb_set_redirected(struct sk_buff *skb, bool from_ingress)
> >   {
> > -#ifdef CONFIG_NET_REDIRECT
> >   	skb->redirected = 1;
> > +#ifdef CONFIG_NET_REDIRECT
> >   	skb->from_ingress = from_ingress;
> >   	if (skb->from_ingress)
> >   		skb->tstamp = 0;
> > @@ -4683,9 +4679,7 @@ static inline void skb_set_redirected(struct sk_buff *skb, bool from_ingress)
> >   static inline void skb_reset_redirect(struct sk_buff *skb)
> >   {
> > -#ifdef CONFIG_NET_REDIRECT
> >   	skb->redirected = 0;
> > -#endif
> >   }
> >   static inline bool skb_csum_is_sctp(struct sk_buff *skb)
> > diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> > index a1a0c4e791c6..274353e2cd70 100644
> > --- a/kernel/bpf/cpumap.c
> > +++ b/kernel/bpf/cpumap.c
> > @@ -16,6 +16,7 @@
> >    * netstack, and assigning dedicated CPUs for this stage.  This
> >    * basically allows for 10G wirespeed pre-filtering via bpf.
> >    */
> > +#include <linux/bitops.h>
> >   #include <linux/bpf.h>
> >   #include <linux/filter.h>
> >   #include <linux/ptr_ring.h>
> > @@ -168,6 +169,49 @@ static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
> >   	}
> >   }
> > +static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
> > +				     struct list_head *listp,
> > +				     struct xdp_cpumap_stats *stats)
> > +{
> > +	struct sk_buff *skb, *tmp;
> > +	struct xdp_buff xdp;
> > +	u32 act;
> > +	int err;
> > +
> > +	if (!rcpu->prog)
> > +		return;
>
> Move this one level out. Why explained below.
>
>
> > +
> > +	list_for_each_entry_safe(skb, tmp, listp, list) {
> > +		act = bpf_prog_run_generic_xdp(skb, &xdp, rcpu->prog);
> > +		switch (act) {
> > +		case XDP_PASS:
> > +			break;
> > +		case XDP_REDIRECT:
> > +			skb_list_del_init(skb);
> > +			err = xdp_do_generic_redirect(skb->dev, skb, &xdp,
> > +						      rcpu->prog);
> > +			if (unlikely(err)) {
> > +				kfree_skb(skb);
> > +				stats->drop++;
> > +			} else {
> > +				stats->redirect++;
> > +			}
> > +			return;
> > +		default:
> > +			bpf_warn_invalid_xdp_action(act);
> > +			fallthrough;
> > +		case XDP_ABORTED:
> > +			trace_xdp_exception(skb->dev, rcpu->prog, act);
> > +			fallthrough;
> > +		case XDP_DROP:
> > +			skb_list_del_init(skb);
> > +			kfree_skb(skb);
> > +			stats->drop++;
> > +			return;
> > +		}
> > +	}
> > +}
> > +
> >   static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >   				    void **frames, int n,
> >   				    struct xdp_cpumap_stats *stats)
> > @@ -179,8 +223,6 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >   	if (!rcpu->prog)
> >   		return n;
> > -	rcu_read_lock_bh();
> > -
>
> Notice the return before doing rcu_read_lock_bh().
>
> Here we try to avoid the extra call to do_softirq() when calling
> rcu_read_unlock_bh.
>
> When RX-napi and cpumap share/run-on the same CPU, activating do_softirq()
> two time in the kthread_cpumap cause RX-napi to get more CPU time to enqueue
> more packets into cpumap.  Thus, cpumap can easier get overloaded.
>
>
> >   	xdp_set_return_frame_no_direct();
> >   	xdp.rxq = &rxq;
> > @@ -227,17 +269,34 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >   		}
> >   	}
> > +	xdp_clear_return_frame_no_direct();
> > +
> > +	return nframes;
> > +}
> > +
> > +#define CPUMAP_BATCH 8
> > +
> > +static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
> > +				int xdp_n, struct xdp_cpumap_stats *stats,
> > +				struct list_head *list)
> > +{
> > +	int nframes;
> > +
> > +	rcu_read_lock_bh();
> > +
> > +	nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, xdp_n, stats);
> > +
> >   	if (stats->redirect)
> > -		xdp_do_flush_map();
> > +		xdp_do_flush();
> > -	xdp_clear_return_frame_no_direct();
> > +	if (unlikely(!list_empty(list)))
> > +		cpu_map_bpf_prog_run_skb(rcpu, list, stats);
> > -	rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
> > +	rcu_read_unlock_bh();
>
> I would like to keep this comment, to help people troubleshooting/understand
> why RX-napi to get more CPU time than kthread.
>
>
> >   	return nframes;
> >   }
> > -#define CPUMAP_BATCH 8
> >   static int cpu_map_kthread_run(void *data)
> >   {
> > @@ -254,9 +313,9 @@ static int cpu_map_kthread_run(void *data)
> >   		struct xdp_cpumap_stats stats = {}; /* zero stats */
> >   		unsigned int kmem_alloc_drops = 0, sched = 0;
> >   		gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
> > +		int i, n, m, nframes, xdp_n;
> >   		void *frames[CPUMAP_BATCH];
> >   		void *skbs[CPUMAP_BATCH];
> > -		int i, n, m, nframes;
> >   		LIST_HEAD(list);
> >   		/* Release CPU reschedule checks */
> > @@ -280,9 +339,20 @@ static int cpu_map_kthread_run(void *data)
> >   		 */
> >   		n = __ptr_ring_consume_batched(rcpu->queue, frames,
> >   					       CPUMAP_BATCH);
> > -		for (i = 0; i < n; i++) {
> > +		for (i = 0, xdp_n = 0; i < n; i++) {
> >   			void *f = frames[i];
> > -			struct page *page = virt_to_page(f);
> > +			struct page *page;
> > +
> > +			if (unlikely(__ptr_test_bit(0, &f))) {
> > +				struct sk_buff *skb = f;
> > +
> > +				__ptr_clear_bit(0, &skb);
> > +				list_add_tail(&skb->list, &list);
> > +				continue;
> > +			}
> > +
> > +			frames[xdp_n++] = f;
> > +			page = virt_to_page(f);
> >   			/* Bring struct page memory area to curr CPU. Read by
> >   			 * build_skb_around via page_is_pfmemalloc(), and when
> > @@ -292,7 +362,7 @@ static int cpu_map_kthread_run(void *data)
> >   		}
> >   		/* Support running another XDP prog on this CPU */
> > -		nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, n, &stats);
> > +		nframes = cpu_map_bpf_prog_run(rcpu, frames, xdp_n, &stats, &list);
> >   		if (nframes) {
> >   			m = kmem_cache_alloc_bulk(skbuff_head_cache, gfp, nframes, skbs);
> >   			if (unlikely(m == 0)) {
> > @@ -330,12 +400,6 @@ static int cpu_map_kthread_run(void *data)
> >   	return 0;
> >   }
> > -bool cpu_map_prog_allowed(struct bpf_map *map)
> > -{
> > -	return map->map_type == BPF_MAP_TYPE_CPUMAP &&
> > -	       map->value_size != offsetofend(struct bpf_cpumap_val, qsize);
> > -}
> > -
> >   static int __cpu_map_load_bpf_program(struct bpf_cpu_map_entry *rcpu, int fd)
> >   {
> >   	struct bpf_prog *prog;
> > @@ -696,6 +760,25 @@ int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp,
> >   	return 0;
> >   }
> > +int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
> > +			     struct sk_buff *skb)
> > +{
> > +	int ret;
> > +
> > +	__skb_pull(skb, skb->mac_len);
> > +	skb_set_redirected(skb, false);
> > +	__ptr_set_bit(0, &skb);
> > +
> > +	ret = ptr_ring_produce(rcpu->queue, skb);
> > +	if (ret < 0)
> > +		goto trace;
> > +
> > +	wake_up_process(rcpu->kthread);
> > +trace:
> > +	trace_xdp_cpumap_enqueue(rcpu->map_id, !ret, !!ret, rcpu->cpu);
> > +	return ret;
> > +}
> > +
> >   void __cpu_map_flush(void)
> >   {
> >   	struct list_head *flush_list = this_cpu_ptr(&cpu_map_flush_list);
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index ad5ab33cbd39..8521936414f2 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -5665,8 +5665,7 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
> >   		 * have a bpf_prog installed on an entry
> >   		 */
> >   		for (i = 0; i < new->aux->used_map_cnt; i++) {
> > -			if (dev_map_can_have_prog(new->aux->used_maps[i]) ||
> > -			    cpu_map_prog_allowed(new->aux->used_maps[i])) {
> > +			if (dev_map_can_have_prog(new->aux->used_maps[i])) {
> >   				mutex_unlock(&new->aux->used_maps_mutex);
> >   				return -EINVAL;
> >   			}
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 0b13d8157a8f..4a21fde3028f 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -4038,8 +4038,12 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
> >   			goto err;
> >   		consume_skb(skb);
> >   		break;
> > +	case BPF_MAP_TYPE_CPUMAP:
> > +		err = cpu_map_generic_redirect(fwd, skb);
> > +		if (unlikely(err))
> > +			goto err;
> > +		break;
> >   	default:
> > -		/* TODO: Handle BPF_MAP_TYPE_CPUMAP */
> >   		err = -EBADRQC;
> >   		goto err;
> >   	}
>
>
> I like the rest :-)
>
> Thanks for working on this!
>
> --Jesper
>

Hopefully addressed both points in the respin, thanks!

--
Kartikeya

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