Commit 2214aab2 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

net_sched: sch_fq: rework fq_gc() to avoid stack canary 



Using kmem_cache_free_bulk() in fq_gc() was not optimal.

1) It needs an array.
2) It is only saving cpu cycles for large batches.

The automatic array forces a stack canary, which is expensive.

In practice fq_gc was finding zero, one or two flows at most
per round.

Remove the array, use kmem_cache_free().

This makes fq_enqueue() smaller and faster.

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-79 (-79)
Function                                     old     new   delta
fq_enqueue                                  1629    1550     -79
Total: Before=24886583, After=24886504, chg -0.00%

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260204190034.76277-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 7acee67a

net/sched/sch_fq.c

+11 −13
Original line number Diff line number Diff line
@@ -245,8 +245,6 @@ static void fq_flow_set_throttled(struct fq_sched_data *q, struct fq_flow *f) 
static struct kmem_cache *fq_flow_cachep __read_mostly;





/* limit number of collected flows per round */

#define FQ_GC_MAX 8

#define FQ_GC_AGE (3*HZ)



static bool fq_gc_candidate(const struct fq_flow *f)
@@ -259,10 +257,9 @@ static void fq_gc(struct fq_sched_data *q, 
		  struct rb_root *root,

		  struct sock *sk)

{

	struct fq_flow *f, *tofree = NULL;

	struct rb_node **p, *parent;

	void *tofree[FQ_GC_MAX];

	struct fq_flow *f;

	int i, fcnt = 0;

	int fcnt;



	p = &root->rb_node;

	parent = NULL;
@@ -274,9 +271,8 @@ static void fq_gc(struct fq_sched_data *q, 
			break;



		if (fq_gc_candidate(f)) {

			tofree[fcnt++] = f;

			if (fcnt == FQ_GC_MAX)

				break;

			f->next = tofree;

			tofree = f;

		}



		if (f->sk > sk)
@@ -285,18 +281,20 @@ static void fq_gc(struct fq_sched_data *q, 
			p = &parent->rb_left;

	}



	if (!fcnt)

	if (!tofree)

		return;



	for (i = fcnt; i > 0; ) {

		f = tofree[--i];

	fcnt = 0;

	while (tofree) {

		f = tofree;

		tofree = f->next;

		rb_erase(&f->fq_node, root);

		kmem_cache_free(fq_flow_cachep, f);

		fcnt++;

	}

	q->flows -= fcnt;

	q->inactive_flows -= fcnt;

	q->stat_gc_flows += fcnt;



	kmem_cache_free_bulk(fq_flow_cachep, fcnt, tofree);

}



/* Fast path can be used if :