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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: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jesper Dangaard Brouer 2017-10-16 12:19:44 +02:00 committed by David S. Miller
parent 1c601d829a
commit f9419f7bd7
2 changed files with 89 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
include/trace/events/xdp.h
View File

@ -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>

24
kernel/bpf/cpumap.c
View File

@ -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);
@ -354,7 +361,9 @@ struct bpf_cpu_map_entry *__cpu_map_entry_alloc(u32 qsize, u32 cpu, int map_id)
if (err)
goto free_queue;
rcpu->qsize = qsize;
rcpu->cpu = cpu;
rcpu->map_id = map_id;
rcpu->qsize = qsize;
/* Setup kthread */
rcpu->kthread = kthread_create_on_node(cpu_map_kthread_run, rcpu, numa,
@ -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;
}