linux-kernel - Re: [PATCH v6 3/3] skb_array: array based FIFO for skbs

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Date:	Thu, 2 Jun 2016 12:27:06 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
	netdev@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	brouer@...hat.com, kvm@...r.kernel.org
Subject: Re: [PATCH v6 3/3] skb_array: array based FIFO for skbs

On Thu, Jun 02, 2016 at 04:17:02PM +0800, Jason Wang wrote:
> 
> 
> On 2016年06月01日 20:54, Michael S. Tsirkin wrote:
> >A simple array based FIFO of pointers.  Intended for net stack so uses
> >skbs for type safety. Implemented as a set of wrappers around ptr_array.
> >
> >Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> >---
> >  include/linux/skb_array.h | 129 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 129 insertions(+)
> >  create mode 100644 include/linux/skb_array.h
> >
> >diff --git a/include/linux/skb_array.h b/include/linux/skb_array.h
> >new file mode 100644
> >index 0000000..cb67076
> >--- /dev/null
> >+++ b/include/linux/skb_array.h
> >@@ -0,0 +1,129 @@
> >+/*
> >+ *	Definitions for the 'struct skb_array' datastructure.
> >+ *
> >+ *	Author:
> >+ *		Michael S. Tsirkin <mst@...hat.com>
> >+ *
> >+ *	Copyright (C) 2016 Red Hat, Inc.
> >+ *
> >+ *	This program is free software; you can redistribute it and/or modify it
> >+ *	under the terms of the GNU General Public License as published by the
> >+ *	Free Software Foundation; either version 2 of the License, or (at your
> >+ *	option) any later version.
> >+ *
> >+ *	Limited-size FIFO of skbs. Can be used more or less whenever
> >+ *	sk_buff_head can be used, except you need to know the queue size in
> >+ *	advance.
> >+ *	Implemented as a type-safe wrapper around ptr_ring.
> >+ */
> >+
> >+#ifndef _LINUX_SKB_ARRAY_H
> >+#define _LINUX_SKB_ARRAY_H 1
> >+
> >+#ifdef __KERNEL__
> >+#include <linux/ptr_ring.h>
> >+#include <linux/skbuff.h>
> >+#endif
> >+
> >+struct skb_array {
> >+	struct ptr_ring ring;
> >+};
> >+
> >+/* Might be slightly faster than skb_array_full below, but callers invoking
> >+ * this in a loop must use a compiler barrier, for example cpu_relax().
> >+ */
> >+static inline bool __skb_array_full(struct skb_array *a)
> >+{
> >+	return __ptr_ring_full(&a->ring);
> >+}
> >+
> >+static inline bool skb_array_full(struct skb_array *a)
> >+{
> >+	return ptr_ring_full(&a->ring);
> >+}
> >+
> >+static inline int skb_array_produce(struct skb_array *a, struct sk_buff *skb)
> >+{
> >+	return ptr_ring_produce(&a->ring, skb);
> >+}
> >+
> >+static inline int skb_array_produce_irq(struct skb_array *a, struct sk_buff *skb)
> >+{
> >+	return ptr_ring_produce_irq(&a->ring, skb);
> >+}
> >+
> >+static inline int skb_array_produce_bh(struct skb_array *a, struct sk_buff *skb)
> >+{
> >+	return ptr_ring_produce_bh(&a->ring, skb);
> >+}
> >+
> >+static inline int skb_array_produce_any(struct skb_array *a, struct sk_buff *skb)
> >+{
> >+	return ptr_ring_produce_any(&a->ring, skb);
> >+}
> >+
> >+/* Might be slightly faster than skb_array_empty below, but callers invoking
> >+ * this in a loop must take care to use a compiler barrier, for example
> >+ * cpu_relax().
> >+ */
> >+static inline bool __skb_array_empty(struct skb_array *a)
> >+{
> >+	return !__ptr_ring_peek(&a->ring);
> >+}
> >+
> >+static inline bool skb_array_empty(struct skb_array *a)
> >+{
> >+	return ptr_ring_empty(&a->ring);
> >+}
> >+
> >+static inline struct sk_buff *skb_array_consume(struct skb_array *a)
> >+{
> >+	return ptr_ring_consume(&a->ring);
> >+}
> >+
> >+static inline struct sk_buff *skb_array_consume_irq(struct skb_array *a)
> >+{
> >+	return ptr_ring_consume_irq(&a->ring);
> >+}
> >+
> >+static inline struct sk_buff *skb_array_consume_any(struct skb_array *a)
> >+{
> >+	return ptr_ring_consume_any(&a->ring);
> >+}
> >+
> >+static inline struct sk_buff *skb_array_consume_bh(struct skb_array *a)
> >+{
> >+	return ptr_ring_consume_bh(&a->ring);
> >+}
> >+
> >+static inline int skb_array_peek_len(struct skb_array *a)
> >+{
> >+	return PTR_RING_PEEK_FIELD(&a->ring, struct sk_buff, len, 0);
> >+}
> 
> An interesting case for tun is peek the length of a tagged packet. In this
> case, len should be increased accordingly. So this simple filed peeking
> won't work.
> 
> Do we need a callback here?

I'd say let's just make it do the right thing wrt vlans.
I'll post v7 with this change.



> >+
> >+static inline int skb_array_peek_len_irq(struct skb_array *a)
> >+{
> >+	return PTR_RING_PEEK_FIELD_IRQ(&a->ring, struct sk_buff, len, 0);
> >+}
> >+
> >+static inline int skb_array_peek_len_bh(struct skb_array *a)
> >+{
> >+	return PTR_RING_PEEK_FIELD_BH(&a->ring, struct sk_buff, len, 0);
> >+}
> >+
> >+static inline int skb_array_peek_len_any(struct skb_array *a)
> >+{
> >+	return PTR_RING_PEEK_FIELD_ANY(&a->ring, struct sk_buff, len, 0);
> >+}
> >+
> >+static inline int skb_array_init(struct skb_array *a, int size, gfp_t gfp)
> >+{
> >+	return ptr_ring_init(&a->ring, size, gfp);
> >+}
> >+
> >+static inline void skb_array_cleanup(struct skb_array *a)
> >+{
> >+	ptr_ring_cleanup(&a->ring);
> >+}
> >+
> >+#endif /* _LINUX_SKB_ARRAY_H  */