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Introduce deferred if_start framework 

The framework provides a means to schedule if_start that will be executed
in softint later. It intends to be used to avoid calling if_start,
especially bpf_mtap, in hardware interrupt.

It adds a dedicated softint to a driver if the driver requests to use the
framework via if_deferred_start_init. The driver can schedule deferred
if_start by if_schedule_deferred_start.

Proposed and discussed on tech-kern and tech-net
This commit is contained in:
ozaki-r 2016-12-08 01:06:35 +00:00
parent 9d8a67c608
commit 0cfa5e16fd
2 changed files with 112 additions and 3 deletions
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108
sys/net/if.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: if.c,v 1.363 2016/12/06 01:23:01 ozaki-r Exp $ */
/* $NetBSD: if.c,v 1.364 2016/12/08 01:06:35 ozaki-r Exp $ */
/*-
* Copyright (c) 1999, 2000, 2001, 2008 The NetBSD Foundation, Inc.
@ -90,7 +90,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: if.c,v 1.363 2016/12/06 01:23:01 ozaki-r Exp $");
__KERNEL_RCSID(0, "$NetBSD: if.c,v 1.364 2016/12/08 01:06:35 ozaki-r Exp $");
#if defined(_KERNEL_OPT)
#include "opt_inet.h"
@ -223,6 +223,16 @@ static int sysctl_percpuq_drops_handler(SYSCTLFN_PROTO);
static void sysctl_percpuq_setup(struct sysctllog **, const char *,
struct if_percpuq *);
struct if_deferred_start {
struct ifnet *ids_ifp;
void (*ids_if_start)(struct ifnet *);
void *ids_si;
};
static void if_deferred_start_softint(void *);
static void if_deferred_start_common(struct ifnet *);
static void if_deferred_start_destroy(struct ifnet *);
#if defined(INET) || defined(INET6)
static void sysctl_net_pktq_setup(struct sysctllog **, int);
#endif
@ -953,6 +963,99 @@ bad:
return;
}
/*
* The deferred if_start framework
*
* The common APIs to defer if_start to softint when if_start is requested
* from a device driver running in hardware interrupt context.
*/
/*
* Call ifp->if_start (or equivalent) in a dedicated softint for
* deferred if_start.
*/
static void
if_deferred_start_softint(void *arg)
{
struct if_deferred_start *ids = arg;
struct ifnet *ifp = ids->ids_ifp;
#ifdef DEBUG
log(LOG_DEBUG, "%s: deferred start on %s\n", __func__,
ifp->if_xname);
#endif
ids->ids_if_start(ifp);
}
/*
* The default callback function for deferred if_start.
*/
static void
if_deferred_start_common(struct ifnet *ifp)
{
if_start_lock(ifp);
}
static inline bool
if_snd_is_used(struct ifnet *ifp)
{
return ifp->if_transmit == NULL || ifp->if_transmit == if_nulltransmit ||
ALTQ_IS_ENABLED(&ifp->if_snd);
}
/*
* Schedule deferred if_start.
*/
void
if_schedule_deferred_start(struct ifnet *ifp)
{
KASSERT(ifp->if_deferred_start != NULL);
if (if_snd_is_used(ifp) && IFQ_IS_EMPTY(&ifp->if_snd))
return;
softint_schedule(ifp->if_deferred_start->ids_si);
}
/*
* Create an instance of deferred if_start. A driver should call the function
* only if the driver needs deferred if_start. Drivers can setup their own
* deferred if_start function via 2nd argument.
*/
void
if_deferred_start_init(struct ifnet *ifp, void (*func)(struct ifnet *))
{
struct if_deferred_start *ids;
ids = kmem_zalloc(sizeof(*ids), KM_SLEEP);
if (ids == NULL)
panic("kmem_zalloc failed");
ids->ids_ifp = ifp;
ids->ids_si = softint_establish(SOFTINT_NET|SOFTINT_MPSAFE,
if_deferred_start_softint, ids);
if (func != NULL)
ids->ids_if_start = func;
else
ids->ids_if_start = if_deferred_start_common;
ifp->if_deferred_start = ids;
}
static void
if_deferred_start_destroy(struct ifnet *ifp)
{
if (ifp->if_deferred_start == NULL)
return;
softint_disestablish(ifp->if_deferred_start->ids_si);
kmem_free(ifp->if_deferred_start, sizeof(*ifp->if_deferred_start));
ifp->if_deferred_start = NULL;
}
/*
* The common interface input routine that is called by device drivers,
@ -1194,6 +1297,7 @@ if_detach(struct ifnet *ifp)
callout_destroy(ifp->if_slowtimo_ch);
kmem_free(ifp->if_slowtimo_ch, sizeof(*ifp->if_slowtimo_ch));
}
if_deferred_start_destroy(ifp);
/*
* Do an if_down() to give protocols a chance to do something.

7
sys/net/if.h
View File

@ -1,4 +1,4 @@
/* $NetBSD: if.h,v 1.229 2016/11/22 02:06:00 ozaki-r Exp $ */
/* $NetBSD: if.h,v 1.230 2016/12/08 01:06:35 ozaki-r Exp $ */
/*-
* Copyright (c) 1999, 2000, 2001 The NetBSD Foundation, Inc.
@ -230,6 +230,7 @@ struct bridge_iflist;
struct callout;
struct krwlock;
struct if_percpuq;
struct if_deferred_start;
typedef unsigned short if_index_t;
@ -342,6 +343,7 @@ typedef struct ifnet {
struct pslist_entry if_pslist_entry;
struct psref_target if_psref;
struct pslist_head if_addr_pslist;
struct if_deferred_start *if_deferred_start;
#endif
} ifnet_t;
@ -989,6 +991,9 @@ void if_percpuq_destroy(struct if_percpuq *);
void
if_percpuq_enqueue(struct if_percpuq *, struct mbuf *);
void if_deferred_start_init(struct ifnet *, void (*)(struct ifnet *));
void if_schedule_deferred_start(struct ifnet *);
void ifa_insert(struct ifnet *, struct ifaddr *);
void ifa_remove(struct ifnet *, struct ifaddr *);