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Message-ID: <1446860278-353064-1-git-send-email-kafai@fb.com>
Date: Fri, 6 Nov 2015 17:37:58 -0800
From: Martin KaFai Lau <kafai@...com>
To: <linux-kernel@...r.kernel.org>
Subject: [RFC] kprobes: Use percpu counter to collect nhit statistics
When doing ebpf+kprobe on some hot TCP functions (e.g.
tcp_rcv_established), the kprobe_dispatcher shows up in 'perf report'.
In kprobe_dispatcher(), there is a lot of cache bouncing
in 'tk->nhit++'. 'tk->nhit' and 'tk->tp.flags' also share
the same cacheline.
perf report (cycles:pp):
8.30% ipv4_dst_check
4.74% copy_user_enhanced_fast_string
3.93% dst_release
2.80% tcp_v4_rcv
2.31% queued_spin_lock_slowpath
2.30% _raw_spin_lock
1.88% mlx4_en_process_rx_cq
1.84% eth_get_headlen
1.81% ip_rcv_finish
~~~~
1.71% kprobe_dispatcher
~~~~
1.55% mlx4_en_xmit
1.09% __probe_kernel_read
perf report after patch:
9.15% ipv4_dst_check
5.00% copy_user_enhanced_fast_string
4.12% dst_release
2.96% tcp_v4_rcv
2.50% _raw_spin_lock
2.39% queued_spin_lock_slowpath
2.11% eth_get_headlen
2.03% mlx4_en_process_rx_cq
1.69% mlx4_en_xmit
1.19% ip_rcv_finish
1.12% __probe_kernel_read
1.02% ehci_hcd_cleanup
Signed-off-by: Martin KaFai Lau <kafai@...com>
---
kernel/trace/trace_kprobe.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c995644..91a441b 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -30,7 +30,7 @@
struct trace_kprobe {
struct list_head list;
struct kretprobe rp; /* Use rp.kp for kprobe use */
- unsigned long nhit;
+ unsigned long * __percpu nhit;
const char *symbol; /* symbol name */
struct trace_probe tp;
};
@@ -274,6 +274,10 @@ static struct trace_kprobe *alloc_trace_kprobe(const char *group,
if (!tk)
return ERR_PTR(ret);
+ tk->nhit = alloc_percpu(unsigned long);
+ if (!tk->nhit)
+ goto error;
+
if (symbol) {
tk->symbol = kstrdup(symbol, GFP_KERNEL);
if (!tk->symbol)
@@ -313,6 +317,7 @@ static struct trace_kprobe *alloc_trace_kprobe(const char *group,
error:
kfree(tk->tp.call.name);
kfree(tk->symbol);
+ free_percpu(tk->nhit);
kfree(tk);
return ERR_PTR(ret);
}
@@ -327,6 +332,7 @@ static void free_trace_kprobe(struct trace_kprobe *tk)
kfree(tk->tp.call.class->system);
kfree(tk->tp.call.name);
kfree(tk->symbol);
+ free_percpu(tk->nhit);
kfree(tk);
}
@@ -874,9 +880,14 @@ static const struct file_operations kprobe_events_ops = {
static int probes_profile_seq_show(struct seq_file *m, void *v)
{
struct trace_kprobe *tk = v;
+ unsigned long nhit = 0;
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ nhit += *per_cpu_ptr(tk->nhit, cpu);
seq_printf(m, " %-44s %15lu %15lu\n",
- trace_event_name(&tk->tp.call), tk->nhit,
+ trace_event_name(&tk->tp.call), nhit,
tk->rp.kp.nmissed);
return 0;
@@ -1225,7 +1236,7 @@ static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs)
{
struct trace_kprobe *tk = container_of(kp, struct trace_kprobe, rp.kp);
- tk->nhit++;
+ raw_cpu_inc(*tk->nhit);
if (tk->tp.flags & TP_FLAG_TRACE)
kprobe_trace_func(tk, regs);
@@ -1242,7 +1253,7 @@ kretprobe_dispatcher(struct kretprobe_instance *ri, struct pt_regs *regs)
{
struct trace_kprobe *tk = container_of(ri->rp, struct trace_kprobe, rp);
- tk->nhit++;
+ raw_cpu_inc(*tk->nhit);
if (tk->tp.flags & TP_FLAG_TRACE)
kretprobe_trace_func(tk, ri, regs);
--
2.5.1
--
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