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bpf: cpumap use ptr_ring_consume_batched

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Move ptr_ring dequeue outside loop, that allocate SKBs and calls network
stack, as these operations that can take some time. The ptr_ring is a
communication channel between CPUs, where we want to reduce/limit any
cacheline bouncing.

Do a concentrated bulk dequeue via ptr_ring_consume_batched, to shorten the
period and times the remote cacheline in ptr_ring is read

Batch size 8 is both to (1) limit BH-disable period, and (2) consume one
cacheline on 64-bit archs. After reducing the BH-disable section further
then we can consider changing this, while still thinking about L1 cacheline
size being active.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jesper Dangaard Brouer 2019-04-12 17:07:32 +02:00 committed by Alexei Starovoitov
parent 00967e84f7
commit 77361825bb
1 changed files with 11 additions and 10 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

21
kernel/bpf/cpumap.c
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@ -240,6 +240,8 @@ static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
}
}
#define CPUMAP_BATCH 8
static int cpu_map_kthread_run(void *data)
{
struct bpf_cpu_map_entry *rcpu = data;
@ -252,8 +254,9 @@ 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, sched = 0;
struct xdp_frame *xdpf;
unsigned int drops = 0, sched = 0;
void *frames[CPUMAP_BATCH];
int i, n;
/* Release CPU reschedule checks */
if (__ptr_ring_empty(rcpu->queue)) {
@ -269,14 +272,16 @@ static int cpu_map_kthread_run(void *data)
sched = cond_resched();
}
/* Process packets in rcpu->queue */
local_bh_disable();
/*
* The bpf_cpu_map_entry is single consumer, with this
* kthread CPU pinned. Lockless access to ptr_ring
* consume side valid as no-resize allowed of queue.
*/
while ((xdpf = __ptr_ring_consume(rcpu->queue))) {
n = ptr_ring_consume_batched(rcpu->queue, frames, CPUMAP_BATCH);
local_bh_disable();
for (i = 0; i < n; i++) {
struct xdp_frame *xdpf = frames[i];
struct sk_buff *skb;
int ret;
@ -290,13 +295,9 @@ static int cpu_map_kthread_run(void *data)
ret = netif_receive_skb_core(skb);
if (ret == NET_RX_DROP)
drops++;
/* Limit BH-disable period */
if (++processed == 8)
break;
}
/* Feedback loop via tracepoint */
trace_xdp_cpumap_kthread(rcpu->map_id, processed, drops, sched);
trace_xdp_cpumap_kthread(rcpu->map_id, n, drops, sched);
local_bh_enable(); /* resched point, may call do_softirq() */
}