[tip: perf/core] uprobes: switch to RCU Tasks Trace flavor for better performance

["tip-bot2 for Andrii Nakryiko" <tip-bot2@linutronix.de>]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     c4d4569c41f9cda745cfd1d8089ea3d3526bafe5
Gitweb:        https://git.kernel.org/tip/c4d4569c41f9cda745cfd1d8089ea3d3526bafe5
Author:        Andrii Nakryiko <andrii@kernel.org>
AuthorDate:    Tue, 03 Sep 2024 10:46:03 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 05 Sep 2024 16:56:15 +02:00

uprobes: switch to RCU Tasks Trace flavor for better performance

This patch switches uprobes SRCU usage to RCU Tasks Trace flavor, which
is optimized for more lightweight and quick readers (at the expense of
slower writers, which for uprobes is a fine tradeof) and has better
performance and scalability with number of CPUs.

Similarly to baseline vs SRCU, we've benchmarked SRCU-based
implementation vs RCU Tasks Trace implementation.

SRCU
====
uprobe-nop      ( 1 cpus):    3.276 ± 0.005M/s  (  3.276M/s/cpu)
uprobe-nop      ( 2 cpus):    4.125 ± 0.002M/s  (  2.063M/s/cpu)
uprobe-nop      ( 4 cpus):    7.713 ± 0.002M/s  (  1.928M/s/cpu)
uprobe-nop      ( 8 cpus):    8.097 ± 0.006M/s  (  1.012M/s/cpu)
uprobe-nop      (16 cpus):    6.501 ± 0.056M/s  (  0.406M/s/cpu)
uprobe-nop      (32 cpus):    4.398 ± 0.084M/s  (  0.137M/s/cpu)
uprobe-nop      (64 cpus):    6.452 ± 0.000M/s  (  0.101M/s/cpu)

uretprobe-nop   ( 1 cpus):    2.055 ± 0.001M/s  (  2.055M/s/cpu)
uretprobe-nop   ( 2 cpus):    2.677 ± 0.000M/s  (  1.339M/s/cpu)
uretprobe-nop   ( 4 cpus):    4.561 ± 0.003M/s  (  1.140M/s/cpu)
uretprobe-nop   ( 8 cpus):    5.291 ± 0.002M/s  (  0.661M/s/cpu)
uretprobe-nop   (16 cpus):    5.065 ± 0.019M/s  (  0.317M/s/cpu)
uretprobe-nop   (32 cpus):    3.622 ± 0.003M/s  (  0.113M/s/cpu)
uretprobe-nop   (64 cpus):    3.723 ± 0.002M/s  (  0.058M/s/cpu)

RCU Tasks Trace
===============
uprobe-nop      ( 1 cpus):    3.396 ± 0.002M/s  (  3.396M/s/cpu)
uprobe-nop      ( 2 cpus):    4.271 ± 0.006M/s  (  2.135M/s/cpu)
uprobe-nop      ( 4 cpus):    8.499 ± 0.015M/s  (  2.125M/s/cpu)
uprobe-nop      ( 8 cpus):   10.355 ± 0.028M/s  (  1.294M/s/cpu)
uprobe-nop      (16 cpus):    7.615 ± 0.099M/s  (  0.476M/s/cpu)
uprobe-nop      (32 cpus):    4.430 ± 0.007M/s  (  0.138M/s/cpu)
uprobe-nop      (64 cpus):    6.887 ± 0.020M/s  (  0.108M/s/cpu)

uretprobe-nop   ( 1 cpus):    2.174 ± 0.001M/s  (  2.174M/s/cpu)
uretprobe-nop   ( 2 cpus):    2.853 ± 0.001M/s  (  1.426M/s/cpu)
uretprobe-nop   ( 4 cpus):    4.913 ± 0.002M/s  (  1.228M/s/cpu)
uretprobe-nop   ( 8 cpus):    5.883 ± 0.002M/s  (  0.735M/s/cpu)
uretprobe-nop   (16 cpus):    5.147 ± 0.001M/s  (  0.322M/s/cpu)
uretprobe-nop   (32 cpus):    3.738 ± 0.008M/s  (  0.117M/s/cpu)
uretprobe-nop   (64 cpus):    4.397 ± 0.002M/s  (  0.069M/s/cpu)

Peak throughput for uprobes increases from 8 mln/s to 10.3 mln/s
(+28%!), and for uretprobes from 5.3 mln/s to 5.8 mln/s (+11%), as we
have more work to do on uretprobes side.

Even single-thread (no contention) performance is slightly better: 3.276
mln/s to 3.396 mln/s (+3.5%) for uprobes, and 2.055 mln/s to 2.174 mln/s
(+5.8%) for uretprobes.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240903174603.3554182-9-andrii@kernel.org
---
 kernel/events/uprobes.c | 38 ++++++++++++++++----------------------
 1 file changed, 16 insertions(+), 22 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4b7e590..a2e6a57 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -26,6 +26,7 @@
 #include <linux/task_work.h>
 #include <linux/shmem_fs.h>
 #include <linux/khugepaged.h>
+#include <linux/rcupdate_trace.h>
 
 #include <linux/uprobes.h>
 
@@ -42,8 +43,6 @@ static struct rb_root uprobes_tree = RB_ROOT;
 static DEFINE_RWLOCK(uprobes_treelock);	/* serialize rbtree access */
 static seqcount_rwlock_t uprobes_seqcount = SEQCNT_RWLOCK_ZERO(uprobes_seqcount, &uprobes_treelock);
 
-DEFINE_STATIC_SRCU(uprobes_srcu);
-
 #define UPROBES_HASH_SZ	13
 /* serialize uprobe->pending_list */
 static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
@@ -652,7 +651,7 @@ static void put_uprobe(struct uprobe *uprobe)
 	delayed_uprobe_remove(uprobe, NULL);
 	mutex_unlock(&delayed_uprobe_lock);
 
-	call_srcu(&uprobes_srcu, &uprobe->rcu, uprobe_free_rcu);
+	call_rcu_tasks_trace(&uprobe->rcu, uprobe_free_rcu);
 }
 
 static __always_inline
@@ -707,7 +706,7 @@ static struct uprobe *find_uprobe_rcu(struct inode *inode, loff_t offset)
 	struct rb_node *node;
 	unsigned int seq;
 
-	lockdep_assert(srcu_read_lock_held(&uprobes_srcu));
+	lockdep_assert(rcu_read_lock_trace_held());
 
 	do {
 		seq = read_seqcount_begin(&uprobes_seqcount);
@@ -935,8 +934,7 @@ static bool filter_chain(struct uprobe *uprobe, struct mm_struct *mm)
 	bool ret = false;
 
 	down_read(&uprobe->consumer_rwsem);
-	list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
-				 srcu_read_lock_held(&uprobes_srcu)) {
+	list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
 		ret = consumer_filter(uc, mm);
 		if (ret)
 			break;
@@ -1157,7 +1155,7 @@ void uprobe_unregister_sync(void)
 	 * unlucky enough caller can free consumer's memory and cause
 	 * handler_chain() or handle_uretprobe_chain() to do an use-after-free.
 	 */
-	synchronize_srcu(&uprobes_srcu);
+	synchronize_rcu_tasks_trace();
 }
 EXPORT_SYMBOL_GPL(uprobe_unregister_sync);
 
@@ -1241,19 +1239,18 @@ EXPORT_SYMBOL_GPL(uprobe_register);
 int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool add)
 {
 	struct uprobe_consumer *con;
-	int ret = -ENOENT, srcu_idx;
+	int ret = -ENOENT;
 
 	down_write(&uprobe->register_rwsem);
 
-	srcu_idx = srcu_read_lock(&uprobes_srcu);
-	list_for_each_entry_srcu(con, &uprobe->consumers, cons_node,
-				 srcu_read_lock_held(&uprobes_srcu)) {
+	rcu_read_lock_trace();
+	list_for_each_entry_rcu(con, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
 		if (con == uc) {
 			ret = register_for_each_vma(uprobe, add ? uc : NULL);
 			break;
 		}
 	}
-	srcu_read_unlock(&uprobes_srcu, srcu_idx);
+	rcu_read_unlock_trace();
 
 	up_write(&uprobe->register_rwsem);
 
@@ -2123,8 +2120,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
 
 	current->utask->auprobe = &uprobe->arch;
 
-	list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
-				 srcu_read_lock_held(&uprobes_srcu)) {
+	list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
 		int rc = 0;
 
 		if (uc->handler) {
@@ -2162,15 +2158,13 @@ handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
 {
 	struct uprobe *uprobe = ri->uprobe;
 	struct uprobe_consumer *uc;
-	int srcu_idx;
 
-	srcu_idx = srcu_read_lock(&uprobes_srcu);
-	list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
-				 srcu_read_lock_held(&uprobes_srcu)) {
+	rcu_read_lock_trace();
+	list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
 		if (uc->ret_handler)
 			uc->ret_handler(uc, ri->func, regs);
 	}
-	srcu_read_unlock(&uprobes_srcu, srcu_idx);
+	rcu_read_unlock_trace();
 }
 
 static struct return_instance *find_next_ret_chain(struct return_instance *ri)
@@ -2255,13 +2249,13 @@ static void handle_swbp(struct pt_regs *regs)
 {
 	struct uprobe *uprobe;
 	unsigned long bp_vaddr;
-	int is_swbp, srcu_idx;
+	int is_swbp;
 
 	bp_vaddr = uprobe_get_swbp_addr(regs);
 	if (bp_vaddr == uprobe_get_trampoline_vaddr())
 		return uprobe_handle_trampoline(regs);
 
-	srcu_idx = srcu_read_lock(&uprobes_srcu);
+	rcu_read_lock_trace();
 
 	uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
 	if (!uprobe) {
@@ -2319,7 +2313,7 @@ static void handle_swbp(struct pt_regs *regs)
 
 out:
 	/* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */
-	srcu_read_unlock(&uprobes_srcu, srcu_idx);
+	rcu_read_unlock_trace();
 }
 
 /*