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Commit f9419f7b authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by David S. Miller
Browse files

bpf: cpumap add tracepoints 



This adds two tracepoint to the cpumap.  One for the enqueue side
trace_xdp_cpumap_enqueue() and one for the kthread dequeue side
trace_xdp_cpumap_kthread().

To mitigate the tracepoint overhead, these are invoked during the
enqueue/dequeue bulking phases, thus amortizing the cost.

The obvious use-cases are for debugging and monitoring.  The
non-intuitive use-case is using these as a feedback loop to know the
system load.  One can imagine auto-scaling by reducing, adding or
activating more worker CPUs on demand.

V4: tracepoint remove time_limit info, instead add sched info

V8: intro struct bpf_cpu_map_entry members cpu+map_id in this patch

Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1c601d82

include/trace/events/xdp.h

+70 −0
Original line number Diff line number Diff line
@@ -150,6 +150,76 @@ DEFINE_EVENT_PRINT(xdp_redirect_template, xdp_redirect_map_err, 
	 trace_xdp_redirect_map_err(dev, xdp, devmap_ifindex(fwd, map),	\

				    err, map, idx)



TRACE_EVENT(xdp_cpumap_kthread,



	TP_PROTO(int map_id, unsigned int processed,  unsigned int drops,

		 int sched),



	TP_ARGS(map_id, processed, drops, sched),



	TP_STRUCT__entry(

		__field(int, map_id)

		__field(u32, act)

		__field(int, cpu)

		__field(unsigned int, drops)

		__field(unsigned int, processed)

		__field(int, sched)

	),



	TP_fast_assign(

		__entry->map_id		= map_id;

		__entry->act		= XDP_REDIRECT;

		__entry->cpu		= smp_processor_id();

		__entry->drops		= drops;

		__entry->processed	= processed;

		__entry->sched	= sched;

	),



	TP_printk("kthread"

		  " cpu=%d map_id=%d action=%s"

		  " processed=%u drops=%u"

		  " sched=%d",

		  __entry->cpu, __entry->map_id,

		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),

		  __entry->processed, __entry->drops,

		  __entry->sched)

);



TRACE_EVENT(xdp_cpumap_enqueue,



	TP_PROTO(int map_id, unsigned int processed,  unsigned int drops,

		 int to_cpu),



	TP_ARGS(map_id, processed, drops, to_cpu),



	TP_STRUCT__entry(

		__field(int, map_id)

		__field(u32, act)

		__field(int, cpu)

		__field(unsigned int, drops)

		__field(unsigned int, processed)

		__field(int, to_cpu)

	),



	TP_fast_assign(

		__entry->map_id		= map_id;

		__entry->act		= XDP_REDIRECT;

		__entry->cpu		= smp_processor_id();

		__entry->drops		= drops;

		__entry->processed	= processed;

		__entry->to_cpu		= to_cpu;

	),



	TP_printk("enqueue"

		  " cpu=%d map_id=%d action=%s"

		  " processed=%u drops=%u"

		  " to_cpu=%d",

		  __entry->cpu, __entry->map_id,

		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),

		  __entry->processed, __entry->drops,

		  __entry->to_cpu)

);



#endif /* _TRACE_XDP_H */



#include <trace/define_trace.h>

kernel/bpf/cpumap.c

+19 −5
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 
#include <linux/workqueue.h>

#include <linux/kthread.h>

#include <linux/capability.h>

#include <trace/events/xdp.h>



#include <linux/netdevice.h>   /* netif_receive_skb_core */

#include <linux/etherdevice.h> /* eth_type_trans */
@@ -43,6 +44,8 @@ struct xdp_bulk_queue { 


/* 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;  /* Queue size placeholder for map lookup */



	/* XDP can run multiple RX-ring queues, need __percpu enqueue store */
@@ -280,15 +283,16 @@ static int cpu_map_kthread_run(void *data) 
	 * kthread_stop signal until queue is empty.

	 */

	while (!kthread_should_stop() || !__ptr_ring_empty(rcpu->queue)) {

		unsigned int processed = 0, drops = 0;

		unsigned int processed = 0, drops = 0, sched = 0;

		struct xdp_pkt *xdp_pkt;



		/* Release CPU reschedule checks */

		if (__ptr_ring_empty(rcpu->queue)) {

			__set_current_state(TASK_INTERRUPTIBLE);

			schedule();

			sched = 1;

		} else {

			cond_resched();

			sched = cond_resched();

		}

		__set_current_state(TASK_RUNNING);
@@ -318,6 +322,9 @@ static int cpu_map_kthread_run(void *data) 
			if (++processed == 8)

				break;

		}

		/* Feedback loop via tracepoint */

		trace_xdp_cpumap_kthread(rcpu->map_id, processed, drops, sched);



		local_bh_enable(); /* resched point, may call do_softirq() */

	}

	__set_current_state(TASK_RUNNING);
@@ -354,6 +361,8 @@ struct bpf_cpu_map_entry *__cpu_map_entry_alloc(u32 qsize, u32 cpu, int map_id) 
	if (err)

		goto free_queue;



	rcpu->cpu    = cpu;

	rcpu->map_id = map_id;

	rcpu->qsize  = qsize;



	/* Setup kthread */
@@ -584,6 +593,8 @@ const struct bpf_map_ops cpu_map_ops = { 
static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,

			     struct xdp_bulk_queue *bq)

{

	unsigned int processed = 0, drops = 0;

	const int to_cpu = rcpu->cpu;

	struct ptr_ring *q;

	int i;
@@ -599,13 +610,16 @@ static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu, 


		err = __ptr_ring_produce(q, xdp_pkt);

		if (err) {

			/* Free xdp_pkt */

			page_frag_free(xdp_pkt);

			drops++;

			page_frag_free(xdp_pkt); /* Free xdp_pkt */

		}

		processed++;

	}

	bq->count = 0;

	spin_unlock(&q->producer_lock);



	/* Feedback loop via tracepoints */

	trace_xdp_cpumap_enqueue(rcpu->map_id, processed, drops, to_cpu);

	return 0;

}