[PATCH] bpf: added the account of BPF running time

[Yunhui Cui]

The following high CPU usage problem is caused by BPF, We found it through
the perf tools.
Children Self 	SharedObject 	Symbol
45.52%	45.51%	[kernel]	[k] native_queued_spin_lock_slowpath
45.35%	0.10%	[kernel]	[k] _raw_spin_lock_irqsave
45.29%	0.01%	[kernel]	[k] bpf_map_update_elem
45.29%	0.02%	[kernel]	[k] htab_map_update_elem

The above problem is caught when bpf_prog is executed, but we cannot
get the load on the system from bpf_progs executed before, and we
cannot monitor the occupancy rate of cpu by BPF all the time.

Currently only the running time of a single bpf_prog is counted in the
/proc/$pid/fdinfo/$fd file. It's impossible to count the occupancy rate
of all bpf_progs on the CPU, because we can't know which processes, and
it is possible that the process has exited.

With the increasing use of BPF function modules, all running bpf_progs may
occupy high CPU usage. So we need to add an item to the /proc/stat file to
observe the CPU usage of BPF from a global perspective.

Signed-off-by: Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>
---
 Documentation/filesystems/proc.rst |  1 +
 fs/proc/stat.c                     | 25 +++++++++++++++++++++++--
 include/linux/filter.h             | 17 +++++++++++++++--
 kernel/bpf/core.c                  |  1 +
 4 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index e7aafc82be99..353f41c3e4eb 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -1477,6 +1477,7 @@ second).  The meanings of the columns are as follows, from left to right:
 - steal: involuntary wait
 - guest: running a normal guest
 - guest_nice: running a niced guest
+- bpf: running in bpf_programs
 
 The "intr" line gives counts of interrupts  serviced since boot time, for each
 of the  possible system interrupts.   The first  column  is the  total of  all
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 4fb8729a68d4..ff8ef959fb4f 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -14,6 +14,8 @@
 #include <linux/irqnr.h>
 #include <linux/sched/cputime.h>
 #include <linux/tick.h>
+#include <linux/filter.h>
+#include <linux/u64_stats_sync.h>
 
 #ifndef arch_irq_stat_cpu
 #define arch_irq_stat_cpu(cpu) 0
@@ -22,6 +24,20 @@
 #define arch_irq_stat() 0
 #endif
 
+DECLARE_PER_CPU(struct bpf_account, bpftime);
+
+static void get_bpf_time(u64 *ns, int cpu)
+{
+	unsigned int start = 0;
+	const struct bpf_account *bact;
+
+	bact = per_cpu_ptr(&bpftime, cpu);
+	do {
+		start = u64_stats_fetch_begin_irq(&bact->syncp);
+		*ns = u64_stats_read(&bact->nsecs);
+	} while (u64_stats_fetch_retry_irq(&bact->syncp, start));
+}
+
 #ifdef arch_idle_time
 
 u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
@@ -112,11 +128,12 @@ static int show_stat(struct seq_file *p, void *v)
 	u64 guest, guest_nice;
 	u64 sum = 0;
 	u64 sum_softirq = 0;
+	u64 bpf_sum, bpf;
 	unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
 	struct timespec64 boottime;
 
 	user = nice = system = idle = iowait =
-		irq = softirq = steal = 0;
+		irq = softirq = steal = bpf = bpf_sum = 0;
 	guest = guest_nice = 0;
 	getboottime64(&boottime);
 	/* shift boot timestamp according to the timens offset */
@@ -127,6 +144,7 @@ static int show_stat(struct seq_file *p, void *v)
 		u64 *cpustat = kcpustat.cpustat;
 
 		kcpustat_cpu_fetch(&kcpustat, i);
+		get_bpf_time(&bpf, i);
 
 		user		+= cpustat[CPUTIME_USER];
 		nice		+= cpustat[CPUTIME_NICE];
@@ -138,6 +156,7 @@ static int show_stat(struct seq_file *p, void *v)
 		steal		+= cpustat[CPUTIME_STEAL];
 		guest		+= cpustat[CPUTIME_GUEST];
 		guest_nice	+= cpustat[CPUTIME_GUEST_NICE];
+		bpf_sum		+= bpf;
 		sum		+= kstat_cpu_irqs_sum(i);
 		sum		+= arch_irq_stat_cpu(i);
 
@@ -160,6 +179,7 @@ static int show_stat(struct seq_file *p, void *v)
 	seq_put_decimal_ull(p, " ", nsec_to_clock_t(steal));
 	seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest));
 	seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest_nice));
+	seq_put_decimal_ull(p, " ", nsec_to_clock_t(bpf_sum));
 	seq_putc(p, '\n');
 
 	for_each_online_cpu(i) {
@@ -167,7 +187,7 @@ static int show_stat(struct seq_file *p, void *v)
 		u64 *cpustat = kcpustat.cpustat;
 
 		kcpustat_cpu_fetch(&kcpustat, i);
-
+		get_bpf_time(&bpf, i);
 		/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
 		user		= cpustat[CPUTIME_USER];
 		nice		= cpustat[CPUTIME_NICE];
@@ -190,6 +210,7 @@ static int show_stat(struct seq_file *p, void *v)
 		seq_put_decimal_ull(p, " ", nsec_to_clock_t(steal));
 		seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest));
 		seq_put_decimal_ull(p, " ", nsec_to_clock_t(guest_nice));
+		seq_put_decimal_ull(p, " ", nsec_to_clock_t(bpf));
 		seq_putc(p, '\n');
 	}
 	seq_put_decimal_ull(p, "intr ", (unsigned long long)sum);
diff --git a/include/linux/filter.h b/include/linux/filter.h
index a5f21dc3c432..9cb072f9e32b 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -565,6 +565,12 @@ struct sk_filter {
 	struct bpf_prog	*prog;
 };
 
+struct bpf_account {
+	u64_stats_t nsecs;
+	struct u64_stats_sync syncp;
+};
+DECLARE_PER_CPU(struct bpf_account, bpftime);
+
 DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 
 typedef unsigned int (*bpf_dispatcher_fn)(const void *ctx,
@@ -577,12 +583,14 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
 					  bpf_dispatcher_fn dfunc)
 {
 	u32 ret;
+	struct bpf_account *bact;
+	unsigned long flags;
+	u64 start = 0;
 
 	cant_migrate();
+	start = sched_clock();
 	if (static_branch_unlikely(&bpf_stats_enabled_key)) {
 		struct bpf_prog_stats *stats;
-		u64 start = sched_clock();
-		unsigned long flags;
 
 		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
 		stats = this_cpu_ptr(prog->stats);
@@ -593,6 +601,11 @@ static __always_inline u32 __bpf_prog_run(const struct bpf_prog *prog,
 	} else {
 		ret = dfunc(ctx, prog->insnsi, prog->bpf_func);
 	}
+	bact = this_cpu_ptr(&bpftime);
+	flags = u64_stats_update_begin_irqsave(&bact->syncp);
+	u64_stats_add(&bact->nsecs, sched_clock() - start);
+	u64_stats_update_end_irqrestore(&bact->syncp, flags);
+
 	return ret;
 }
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index c1e10d088dbb..445ac1c6c01a 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -618,6 +618,7 @@ static const struct latch_tree_ops bpf_tree_ops = {
 	.comp	= bpf_tree_comp,
 };
 
+DEFINE_PER_CPU(struct bpf_account, bpftime);
 static DEFINE_SPINLOCK(bpf_lock);
 static LIST_HEAD(bpf_kallsyms);
 static struct latch_tree_root bpf_tree __cacheline_aligned;
-- 
2.20.1