From: Eric Dumazet <dada1@cosmosbay•com>
To: Neil Horman <nhorman@tuxdriver•com>
Cc: netdev@vger•kernel.org, davem@davemloft•net
Subject: Re: [PATCH] dropmon: add ability to detect when hardware drops rx packets
Date: Sat, 09 May 2009 08:30:35 +0200 [thread overview]
Message-ID: <4A05230B.6070806@cosmosbay.com> (raw)
In-Reply-To: <20090508195026.GB13017@hmsreliant.think-freely.org>
Neil Horman a écrit :
> Hey all-
> A few weeks back I sent out an RFC in which I proposed that I could
> extend dropwatch to detect drops in hardware by adding a napi poll tracepoint,
> using that as an indicator that I should periodically check the stats to see if
> the rx drop counter had changed. Having not had any negative feedback to that
> proposal, heres the patch. I've tested it and it seems to work fairly well.
> Neil
>
>
> Patch to add the ability to detect drops in hardware interfaces via dropwatch.
> Adds a tracepoint to net_rx_action to signal everytime a napi instance is
> polled. The dropmon code then periodically checks to see if the rx_frames
> counter has changed, and if so, adds a drop notification to the netlink
> protocol, using the reserved all-0's vector to indicate the drop location was in
> hardware, rather than somewhere in the code.
>
> Signed-off-by: Neil Horman <nhorman@tuxdriver•com>
>
Hi Neil
I dont fully understand your patch, but at least have some questions
about rcu stuff.
>
> include/linux/net_dropmon.h | 7 ++
> include/trace/napi.h | 11 ++++
> net/core/dev.c | 5 +-
> net/core/drop_monitor.c | 107 ++++++++++++++++++++++++++++++++++++++++++--
> net/core/net-traces.c | 4 +
> net/core/netpoll.c | 2
> 6 files changed, 131 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/net_dropmon.h b/include/linux/net_dropmon.h
> index 0217fb8..9addc62 100644
> --- a/include/linux/net_dropmon.h
> +++ b/include/linux/net_dropmon.h
> @@ -8,6 +8,13 @@ struct net_dm_drop_point {
> __u32 count;
> };
>
> +#define is_drop_point_hw(x) do {\
> + int ____i, ____j;\
> + for (____i = 0; ____i < 8; i ____i++)\
> + ____j |= x[____i];\
> + ____j;\
> +} while (0)
> +
> #define NET_DM_CFG_VERSION 0
> #define NET_DM_CFG_ALERT_COUNT 1
> #define NET_DM_CFG_ALERT_DELAY 2
> diff --git a/include/trace/napi.h b/include/trace/napi.h
> new file mode 100644
> index 0000000..7c39eb7
> --- /dev/null
> +++ b/include/trace/napi.h
> @@ -0,0 +1,11 @@
> +#ifndef _TRACE_NAPI_H_
> +#define _TRACE_NAPI_H_
> +
> +#include <linux/skbuff.h>
> +#include <linux/tracepoint.h>
> +
> +DECLARE_TRACE(napi_poll,
> + TP_PROTO(struct napi_struct *napi),
> + TP_ARGS(napi));
> +
> +#endif
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 637ea71..165979c 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -126,6 +126,7 @@
> #include <linux/in.h>
> #include <linux/jhash.h>
> #include <linux/random.h>
> +#include <trace/napi.h>
>
> #include "net-sysfs.h"
>
> @@ -2763,8 +2764,10 @@ static void net_rx_action(struct softirq_action *h)
> * accidently calling ->poll() when NAPI is not scheduled.
> */
> work = 0;
> - if (test_bit(NAPI_STATE_SCHED, &n->state))
> + if (test_bit(NAPI_STATE_SCHED, &n->state)) {
> work = n->poll(n, weight);
> + trace_napi_poll(n);
> + }
>
> WARN_ON_ONCE(work > weight);
>
> diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
> index 2797b71..538c1d4 100644
> --- a/net/core/drop_monitor.c
> +++ b/net/core/drop_monitor.c
> @@ -22,8 +22,10 @@
> #include <linux/timer.h>
> #include <linux/bitops.h>
> #include <net/genetlink.h>
> +#include <net/netevent.h>
>
> #include <trace/skb.h>
> +#include <trace/napi.h>
>
> #include <asm/unaligned.h>
>
> @@ -38,7 +40,7 @@ static void send_dm_alert(struct work_struct *unused);
> * and the work handle that will send up
> * netlink alerts
> */
> -struct sock *dm_sock;
> +static int trace_state = TRACE_OFF;
>
> struct per_cpu_dm_data {
> struct work_struct dm_alert_work;
> @@ -47,6 +49,12 @@ struct per_cpu_dm_data {
> struct timer_list send_timer;
> };
>
> +struct dm_hw_stat_delta {
> + struct net_device *dev;
> + struct list_head list;
> + unsigned long last_drop_val;
> +};
> +
> static struct genl_family net_drop_monitor_family = {
> .id = GENL_ID_GENERATE,
> .hdrsize = 0,
> @@ -59,7 +67,8 @@ static DEFINE_PER_CPU(struct per_cpu_dm_data, dm_cpu_data);
>
> static int dm_hit_limit = 64;
> static int dm_delay = 1;
> -
> +static unsigned long dm_hw_check_delta = 2*HZ;
> +static LIST_HEAD(hw_stats_list);
>
> static void reset_per_cpu_data(struct per_cpu_dm_data *data)
> {
> @@ -115,7 +124,7 @@ static void sched_send_work(unsigned long unused)
> schedule_work(&data->dm_alert_work);
> }
>
> -static void trace_kfree_skb_hit(struct sk_buff *skb, void *location)
> +static void trace_drop_common(struct sk_buff *skb, void *location)
> {
> struct net_dm_alert_msg *msg;
> struct nlmsghdr *nlh;
> @@ -159,18 +168,59 @@ out:
> return;
> }
>
> +static void trace_kfree_skb_hit(struct sk_buff *skb, void *location)
> +{
> + trace_drop_common(skb, location);
> +}
> +
> +static void trace_napi_poll_hit(struct napi_struct *napi)
> +{
> + struct dm_hw_stat_delta *new_stat;
> +
> + /*
> + * Ratelimit our check time to dm_hw_check_delta jiffies
> + */
> + if (!time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta))
> + return;
> +
> + list_for_each_entry_rcu(new_stat, &hw_stats_list, list) {
> + if ((new_stat->dev == napi->dev) &&
> + (napi->dev->stats.rx_dropped != new_stat->last_drop_val)) {
> + trace_drop_common(NULL, NULL);
> + new_stat->last_drop_val = napi->dev->stats.rx_dropped;
> + break;
> + }
> + }
> +}
> +
> +
> static int set_all_monitor_traces(int state)
> {
> int rc = 0;
> + struct dm_hw_stat_delta *new_stat = NULL;
>
> switch (state) {
> case TRACE_ON:
> rc |= register_trace_kfree_skb(trace_kfree_skb_hit);
> + rc |= register_trace_napi_poll(trace_napi_poll_hit);
> break;
> case TRACE_OFF:
> rc |= unregister_trace_kfree_skb(trace_kfree_skb_hit);
> + rc |= unregister_trace_napi_poll(trace_napi_poll_hit);
>
> tracepoint_synchronize_unregister();
> +
> + /*
> + * Clean the device list
> + */
> + rcu_read_lock();
> + list_for_each_entry_rcu(new_stat, &hw_stats_list, list) {
> + if (new_stat->dev == NULL) {
> + list_del_rcu(&new_stat->list);
> + kfree(new_stat);
I can't see how list_del_rcu(&new_stat->list) can be followed by kfree(new_stat)
safely. You need a grace period between two operations. That can be done
with call_rcu() helper.
Also, rcu_read_lock()/rcu_read_unlock() is not the proper locking pragmas
needed here. multiple writers are/should be forbidden here. If caller already
does a locking, then no additional locking is needed here.
> + }
> + }
> + rcu_read_unlock();
> break;
> default:
> rc = 1;
> @@ -179,6 +229,7 @@ static int set_all_monitor_traces(int state)
>
> if (rc)
> return -EINPROGRESS;
> + trace_state = state;
> return rc;
> }
>
> @@ -204,6 +255,43 @@ static int net_dm_cmd_trace(struct sk_buff *skb,
> return -ENOTSUPP;
> }
>
> +int dropmon_net_event(struct notifier_block *ev_block,
> + unsigned long event, void *ptr)
> +{
> + struct net_device *dev = ptr;
> + struct dm_hw_stat_delta *new_stat = NULL;
> +
> +
> + switch (event) {
> + case NETDEV_REGISTER:
> + new_stat = kzalloc(sizeof(struct dm_hw_stat_delta), GFP_KERNEL);
> +
> + if (!new_stat)
> + goto out;
> +
> + new_stat->dev = dev;
> + rcu_read_lock();
same point here, rcu_read_lock is not the proper way to protect the list.
> + list_add_rcu(&new_stat->list, &hw_stats_list);
> + rcu_read_unlock();
> + break;
> + case NETDEV_UNREGISTER:
> + list_for_each_entry_rcu(new_stat, &hw_stats_list, list) {
> + if (new_stat->dev == dev)
> + new_stat->dev = NULL;
> + break;
> + }
> +
> + if (trace_state == TRACE_OFF) {
> + rcu_read_lock();
> + list_del_rcu(&new_stat->list);
> + rcu_read_unlock();
> + kfree(new_stat);
same probleme here. If rcu is used, then you need a grace period.
> + }
> + break;
> + }
> +out:
> + return NOTIFY_DONE;
> +}
>
> static struct genl_ops dropmon_ops[] = {
> {
> @@ -220,6 +308,10 @@ static struct genl_ops dropmon_ops[] = {
> },
> };
>
> +static struct notifier_block dropmon_net_notifier = {
> + .notifier_call = dropmon_net_event
> +};
> +
> static int __init init_net_drop_monitor(void)
> {
> int cpu;
> @@ -243,12 +335,18 @@ static int __init init_net_drop_monitor(void)
> ret = genl_register_ops(&net_drop_monitor_family,
> &dropmon_ops[i]);
> if (ret) {
> - printk(KERN_CRIT "failed to register operation %d\n",
> + printk(KERN_CRIT "Failed to register operation %d\n",
> dropmon_ops[i].cmd);
> goto out_unreg;
> }
> }
>
> + rc = register_netdevice_notifier(&dropmon_net_notifier);
> + if (rc < 0) {
> + printk(KERN_CRIT "Failed to register netdevice notifier\n");
> + goto out_unreg;
> + }
> +
> rc = 0;
>
> for_each_present_cpu(cpu) {
> @@ -259,6 +357,7 @@ static int __init init_net_drop_monitor(void)
> data->send_timer.data = cpu;
> data->send_timer.function = sched_send_work;
> }
> +
> goto out;
>
> out_unreg:
> diff --git a/net/core/net-traces.c b/net/core/net-traces.c
> index c8fb456..b07b25b 100644
> --- a/net/core/net-traces.c
> +++ b/net/core/net-traces.c
> @@ -20,6 +20,7 @@
> #include <linux/netlink.h>
> #include <linux/net_dropmon.h>
> #include <trace/skb.h>
> +#include <trace/napi.h>
>
> #include <asm/unaligned.h>
> #include <asm/bitops.h>
> @@ -27,3 +28,6 @@
>
> DEFINE_TRACE(kfree_skb);
> EXPORT_TRACEPOINT_SYMBOL_GPL(kfree_skb);
> +
> +DEFINE_TRACE(napi_poll);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(napi_poll);
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
> index b5873bd..446d3ba 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -24,6 +24,7 @@
> #include <net/tcp.h>
> #include <net/udp.h>
> #include <asm/unaligned.h>
> +#include <trace/napi.h>
>
> /*
> * We maintain a small pool of fully-sized skbs, to make sure the
> @@ -137,6 +138,7 @@ static int poll_one_napi(struct netpoll_info *npinfo,
> set_bit(NAPI_STATE_NPSVC, &napi->state);
>
> work = napi->poll(napi, budget);
> + trace_napi_poll(napi->dev);
>
> clear_bit(NAPI_STATE_NPSVC, &napi->state);
> atomic_dec(&trapped);
>
next prev parent reply other threads:[~2009-05-09 6:30 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-08 19:50 [PATCH] dropmon: add ability to detect when hardware drops rx packets Neil Horman
2009-05-09 6:30 ` Eric Dumazet [this message]
2009-05-09 18:07 ` Neil Horman
2009-05-12 16:30 ` Neil Horman
2009-05-13 18:23 ` [PATCH] dropmon: add ability to detect when hardware drops rxpackets Paul E. McKenney
2009-05-14 0:45 ` Neil Horman
2009-05-14 1:03 ` [PATCH] dropmon: add ability to detect when hardware dropsrxpackets Paul E. McKenney
2009-05-14 12:33 ` Neil Horman
2009-05-14 12:44 ` Jiri Pirko
2009-05-14 16:17 ` [PATCH] dropmon: add ability to detect when hardwaredropsrxpackets Paul E. McKenney
2009-05-14 17:29 ` [PATCH] dropmon: add ability to detect when hardware dropsrxpackets Neil Horman
2009-05-15 5:49 ` Jarek Poplawski
2009-05-15 11:01 ` Neil Horman
2009-05-15 11:12 ` Jarek Poplawski
2009-05-15 11:15 ` Neil Horman
2009-05-15 11:40 ` Jarek Poplawski
2009-05-16 0:07 ` Paul E. McKenney
2009-05-15 6:51 ` Jiri Pirko
2009-05-15 7:37 ` Eric Dumazet
2009-05-15 11:12 ` Neil Horman
2009-05-15 10:59 ` Neil Horman
2009-05-15 11:27 ` Jiri Pirko
2009-05-15 16:07 ` Neil Horman
2009-05-15 18:11 ` Eric Dumazet
2009-05-15 18:23 ` Stephen Hemminger
2009-05-15 19:53 ` Neil Horman
2009-05-15 19:23 ` Neil Horman
2009-05-16 12:40 ` Neil Horman
2009-05-18 14:46 ` Neil Horman
2009-05-21 7:17 ` David Miller
2009-05-21 17:36 ` Neil Horman
2009-05-21 22:15 ` David Miller
2009-05-22 0:09 ` Neil Horman
2009-05-15 18:18 ` Stephen Hemminger
2009-05-15 19:12 ` Neil Horman
2009-05-14 16:18 ` [PATCH] dropmon: add ability to detect when hardwaredropsrxpackets Paul E. McKenney
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