On Thu, Sep 28, 2017 at 02:57:08PM +0200, Jesper Dangaard Brouer wrote:
> The 'cpumap' is primary used as a backend map for XDP BPF helper
> call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.
>
> This patch implement the main part of the map. It is not connected to
> the XDP redirect system yet, and no SKB allocation are done yet.
>
> The main concern in this patch is to ensure the datapath can run
> without any locking. This adds complexity to the setup and tear-down
> procedure, which assumptions are extra carefully documented in the
> code comments.
>
> Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
> ---
> include/linux/bpf_types.h | 1
> include/uapi/linux/bpf.h | 1
> kernel/bpf/Makefile | 1
> kernel/bpf/cpumap.c | 547
> ++++++++++++++++++++++++++++++++++++++++
> kernel/bpf/syscall.c | 8 +
> tools/include/uapi/linux/bpf.h | 1
> 6 files changed, 558 insertions(+), 1 deletion(-)
> create mode 100644 kernel/bpf/cpumap.c
>
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index 6f1a567667b8..814c1081a4a9 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -41,4 +41,5 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_DEVMAP, dev_map_ops)
> #ifdef CONFIG_STREAM_PARSER
> BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKMAP, sock_map_ops)
> #endif
> +BPF_MAP_TYPE(BPF_MAP_TYPE_CPUMAP, cpu_map_ops)
> #endif
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index e43491ac4823..f14e15702533 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -111,6 +111,7 @@ enum bpf_map_type {
> BPF_MAP_TYPE_HASH_OF_MAPS,
> BPF_MAP_TYPE_DEVMAP,
> BPF_MAP_TYPE_SOCKMAP,
> + BPF_MAP_TYPE_CPUMAP,
> };
>
> enum bpf_prog_type {
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 897daa005b23..dba0bd33a43c 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -4,6 +4,7 @@ obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o
> helpers.o tnum.o
> obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o
> bpf_lru_list.o lpm_trie.o map_in_map.o
> ifeq ($(CONFIG_NET),y)
> obj-$(CONFIG_BPF_SYSCALL) += devmap.o
> +obj-$(CONFIG_BPF_SYSCALL) += cpumap.o
> ifeq ($(CONFIG_STREAM_PARSER),y)
> obj-$(CONFIG_BPF_SYSCALL) += sockmap.o
> endif
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> new file mode 100644
> index 000000000000..f0948af82e65
> --- /dev/null
> +++ b/kernel/bpf/cpumap.c
> @@ -0,0 +1,547 @@
> +/* bpf/cpumap.c
> + *
> + * Copyright (c) 2017 Jesper Dangaard Brouer, Red Hat Inc.
> + * Released under terms in GPL version 2. See COPYING.
> + */
> +
> +/* The 'cpumap' is primary used as a backend map for XDP BPF helper
> + * call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.
> + *
> + * Unlike devmap which redirect XDP frames out another NIC device,
> + * this map type redirect raw XDP frames to another CPU. The remote
> + * CPU will do SKB-allocation and call the normal network stack.
> + *
> + * This is a scalability and isolation mechanism, that allow
> + * separating the early driver network XDP layer, from the rest of the
> + * netstack, and assigning dedicated CPUs for this stage. This
> + * basically allows for 10G wirespeed pre-filtering via bpf.
> + */
> +#include <linux/bpf.h>
> +#include <linux/filter.h>
> +#include <linux/ptr_ring.h>
> +
> +#include <linux/sched.h>
> +#include <linux/workqueue.h>
> +#include <linux/kthread.h>
> +
> +/*
> + * General idea: XDP packets getting XDP redirected to another CPU,
> + * will maximum be stored/queued for one driver ->poll() call. It is
> + * guaranteed that setting flush bit and flush operation happen on
> + * same CPU. Thus, cpu_map_flush operation can deduct via this_cpu_ptr()
> + * which queue in bpf_cpu_map_entry contains packets.
> + */
> +
> +#define CPU_MAP_BULK_SIZE 8 /* 8 == one cacheline on 64-bit archs */
> +struct xdp_bulk_queue {
> + void *q[CPU_MAP_BULK_SIZE];
> + unsigned int count;
> +};
> +
> +/* Struct for every remote "destination" CPU in map */
> +struct bpf_cpu_map_entry {
> + u32 cpu; /* kthread CPU and map index */
> + int map_id; /* Back reference to map */
> + u32 qsize; /* Redundant queue size for map lookup */
> +
> + /* XDP can run multiple RX-ring queues, need __percpu enqueue store */
> + struct xdp_bulk_queue __percpu *bulkq;
> +
> + /* Queue with potential multi-producers, and single-consumer kthread */
> + struct ptr_ring *queue;
> + struct task_struct *kthread;
> + struct work_struct kthread_stop_wq;
> +
> + atomic_t refcnt; /* Control when this struct can be free'ed */
> + struct rcu_head rcu;
> +};
> +
> +struct bpf_cpu_map {
> + struct bpf_map map;
> + /* Below members specific for map type */
> + struct bpf_cpu_map_entry **cpu_map;
> + unsigned long __percpu *flush_needed;
> +};
> +
> +static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,
> + struct xdp_bulk_queue *bq);
> +
> +static u64 cpu_map_bitmap_size(const union bpf_attr *attr)
> +{
> + return BITS_TO_LONGS(attr->max_entries) * sizeof(unsigned long);
> +}
> +
> +static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
> +{
> + struct bpf_cpu_map *cmap;
> + u64 cost;
> + int err;
> +
> + /* check sanity of attributes */
> + if (attr->max_entries == 0 || attr->key_size != 4 ||
> + attr->value_size != 4 || attr->map_flags & ~BPF_F_NUMA_NODE)
> + return ERR_PTR(-EINVAL);
> +
> + cmap = kzalloc(sizeof(*cmap), GFP_USER);
> + if (!cmap)
> + return ERR_PTR(-ENOMEM);
> +
> + /* mandatory map attributes */
> + cmap->map.map_type = attr->map_type;
> + cmap->map.key_size = attr->key_size;
> + cmap->map.value_size = attr->value_size;
> + cmap->map.max_entries = attr->max_entries;
> + cmap->map.map_flags = attr->map_flags;
> + cmap->map.numa_node = bpf_map_attr_numa_node(attr);
> +
> + /* make sure page count doesn't overflow */
> + cost = (u64) cmap->map.max_entries * sizeof(struct bpf_cpu_map_entry *);
> + cost += cpu_map_bitmap_size(attr) * num_possible_cpus();
> + if (cost >= U32_MAX - PAGE_SIZE)
> + goto free_cmap;
> + cmap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
> +
> + /* if map size is larger than memlock limit, reject it early */
> + err = bpf_map_precharge_memlock(cmap->map.pages);
> + if (err)
> + goto free_cmap;
> +
> + /* A per cpu bitfield with a bit per possible CPU in map */
> + cmap->flush_needed = __alloc_percpu(cpu_map_bitmap_size(attr),
> + __alignof__(unsigned long));
> + if (!cmap->flush_needed)
> + goto free_cmap;
> +
> + /* Alloc array for possible remote "destination" CPUs */
> + cmap->cpu_map = bpf_map_area_alloc(cmap->map.max_entries *
> + sizeof(struct bpf_cpu_map_entry *),
> + cmap->map.numa_node);
> + if (!cmap->cpu_map)
> + goto free_cmap;
> +
> + return &cmap->map;
> +free_cmap:
> + free_percpu(cmap->flush_needed);
> + kfree(cmap);
> + return ERR_PTR(-ENOMEM);
> +}
> +
> +void __cpu_map_queue_destructor(void *ptr)
> +{
> + /* For now, just catch this as an error */
> + if (!ptr)
> + return;
> + pr_err("ERROR: %s() cpu_map queue was not empty\n", __func__);
> + page_frag_free(ptr);
> +}
> +
> +static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
> +{
> + if (atomic_dec_and_test(&rcpu->refcnt)) {
> + /* The queue should be empty at this point */
> + ptr_ring_cleanup(rcpu->queue, __cpu_map_queue_destructor);
> + kfree(rcpu->queue);
> + kfree(rcpu);
> + }
> +}
> +
> +static void get_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
> +{
> + atomic_inc(&rcpu->refcnt);
> +}
> +
> +/* called from workqueue, to workaround syscall using preempt_disable */
> +static void cpu_map_kthread_stop(struct work_struct *work)
> +{
> + struct bpf_cpu_map_entry *rcpu;
> +
> + rcpu = container_of(work, struct bpf_cpu_map_entry, kthread_stop_wq);
> + synchronize_rcu(); /* wait for flush in __cpu_map_entry_free() */
> + kthread_stop(rcpu->kthread); /* calls put_cpu_map_entry */
> +}
> +
> +static int cpu_map_kthread_run(void *data)
> +{
> + struct bpf_cpu_map_entry *rcpu = data;
> +
> + set_current_state(TASK_INTERRUPTIBLE);
> + while (!kthread_should_stop()) {
> + struct xdp_pkt *xdp_pkt;
> +
> + schedule();
> + /* Do work */
> + while ((xdp_pkt = ptr_ring_consume(rcpu->queue))) {
> + /* For now just "refcnt-free" */
> + page_frag_free(xdp_pkt);
> + }
> + __set_current_state(TASK_INTERRUPTIBLE);
> + }
> + put_cpu_map_entry(rcpu);
> +
> + __set_current_state(TASK_RUNNING);
> + return 0;
> +}
> +
> +struct bpf_cpu_map_entry *__cpu_map_entry_alloc(u32 qsize, u32 cpu, int
> map_id)
> +{
> + gfp_t gfp = GFP_ATOMIC|__GFP_NOWARN;
> + struct bpf_cpu_map_entry *rcpu;
> + int numa, err;
> +
> + /* Have map->numa_node, but choose node of redirect target CPU */
> + numa = cpu_to_node(cpu);
> +
> + rcpu = kzalloc_node(sizeof(*rcpu), gfp, numa);
> + if (!rcpu)
> + return NULL;
> +
> + /* Alloc percpu bulkq */
> + rcpu->bulkq = __alloc_percpu_gfp(sizeof(*rcpu->bulkq),
> + sizeof(void *), gfp);
> + if (!rcpu->bulkq)
> + goto fail;
> +
> + /* Alloc queue */
> + rcpu->queue = kzalloc_node(sizeof(*rcpu->queue), gfp, numa);
> + if (!rcpu->queue)
> + goto fail;
> +
> + err = ptr_ring_init(rcpu->queue, qsize, gfp);
> + if (err)
> + goto fail;
> + rcpu->qsize = qsize;
> +
> + /* Setup kthread */
> + rcpu->kthread = kthread_create_on_node(cpu_map_kthread_run, rcpu, numa,
> + "cpumap/%d/map:%d", cpu, map_id);
> + if (IS_ERR(rcpu->kthread))
> + goto fail;
> +
> + /* Make sure kthread runs on a single CPU */
> + kthread_bind(rcpu->kthread, cpu);
is there a check that max_entries <= num_possible_cpu ? I couldn't find it.
otherwise it will be binding to impossible cpu?
> + wake_up_process(rcpu->kthread);
In general the whole thing looks like 'threaded NAPI' that Hannes was
proposing some time back. I liked it back then and I like it now.
I don't remember what were the objections back then.
Something scheduler related?
Adding Hannes.
Still curious about the questions I asked in the other thread
on what's causing it to be so much better than RPS
