Patchwork [v2,5/5] net: Add Open vSwitch kernel components.

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Submitter stephen hemminger
Date Nov. 21, 2011, 9:59 p.m.
Message ID <20111121135955.571254b1@nehalam.linuxnetplumber.net>
Download mbox | patch
Permalink /patch/126951/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

stephen hemminger - Nov. 21, 2011, 9:59 p.m.
On Mon, 21 Nov 2011 13:30:29 -0800
Jesse Gross <jesse@nicira.com> wrote:

> +/**
> + *	vport_record_error - indicate device error to generic stats layer
> + *
> + * @vport: vport that encountered the error
> + * @err_type: one of enum vport_err_type types to indicate the error type
> + *
> + * If using the vport generic stats layer indicate that an error of the given
> + * type has occured.
> + */
> +void vport_record_error(struct vport *vport, enum vport_err_type err_type)
> +{
> +	spin_lock(&vport->stats_lock);

Sorry for over analyzing this... but I don't think the stats_lock
is necessary either. The only thing it is protecting is against 64 bit
wrap. If you used another u64_stat_sync for that one, it could be eliminated.

Maybe?


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Jesse Gross - Nov. 21, 2011, 11:18 p.m.
On Mon, Nov 21, 2011 at 1:59 PM, Stephen Hemminger
<shemminger@vyatta.com> wrote:
> On Mon, 21 Nov 2011 13:30:29 -0800
> Jesse Gross <jesse@nicira.com> wrote:
>
>> +/**
>> + *   vport_record_error - indicate device error to generic stats layer
>> + *
>> + * @vport: vport that encountered the error
>> + * @err_type: one of enum vport_err_type types to indicate the error type
>> + *
>> + * If using the vport generic stats layer indicate that an error of the given
>> + * type has occured.
>> + */
>> +void vport_record_error(struct vport *vport, enum vport_err_type err_type)
>> +{
>> +     spin_lock(&vport->stats_lock);
>
> Sorry for over analyzing this... but I don't think the stats_lock
> is necessary either. The only thing it is protecting is against 64 bit
> wrap. If you used another u64_stat_sync for that one, it could be eliminated.
>
> Maybe?

The reason for stats_lock is that the error stats are not expected to
be contended so in order to save some memory they're not per-cpu and
we just use a spin lock to protect them.
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stephen hemminger - Nov. 21, 2011, 11:25 p.m.
On Mon, 21 Nov 2011 15:18:43 -0800
Jesse Gross <jesse@nicira.com> wrote:

> On Mon, Nov 21, 2011 at 1:59 PM, Stephen Hemminger
> <shemminger@vyatta.com> wrote:
> > On Mon, 21 Nov 2011 13:30:29 -0800
> > Jesse Gross <jesse@nicira.com> wrote:
> >
> >> +/**
> >> + *   vport_record_error - indicate device error to generic stats layer
> >> + *
> >> + * @vport: vport that encountered the error
> >> + * @err_type: one of enum vport_err_type types to indicate the error type
> >> + *
> >> + * If using the vport generic stats layer indicate that an error of the given
> >> + * type has occured.
> >> + */
> >> +void vport_record_error(struct vport *vport, enum vport_err_type err_type)
> >> +{
> >> +     spin_lock(&vport->stats_lock);
> >
> > Sorry for over analyzing this... but I don't think the stats_lock
> > is necessary either. The only thing it is protecting is against 64 bit
> > wrap. If you used another u64_stat_sync for that one, it could be eliminated.
> >
> > Maybe?
> 
> The reason for stats_lock is that the error stats are not expected to
> be contended so in order to save some memory they're not per-cpu and
> we just use a spin lock to protect them.

Assignment or increment of native type size (64 bit on 64 bit cpu)
is always atomic.
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=?ISO-8859-2?Q?Micha=B3_Miros=B3aw?= - Nov. 21, 2011, 11:49 p.m.
2011/11/22 Stephen Hemminger <shemminger@vyatta.com>:
> On Mon, 21 Nov 2011 15:18:43 -0800
> Jesse Gross <jesse@nicira.com> wrote:
>
>> On Mon, Nov 21, 2011 at 1:59 PM, Stephen Hemminger
>> <shemminger@vyatta.com> wrote:
>> > On Mon, 21 Nov 2011 13:30:29 -0800
>> > Jesse Gross <jesse@nicira.com> wrote:
>> >
>> >> +/**
>> >> + *   vport_record_error - indicate device error to generic stats layer
>> >> + *
>> >> + * @vport: vport that encountered the error
>> >> + * @err_type: one of enum vport_err_type types to indicate the error type
>> >> + *
>> >> + * If using the vport generic stats layer indicate that an error of the given
>> >> + * type has occured.
>> >> + */
>> >> +void vport_record_error(struct vport *vport, enum vport_err_type err_type)
>> >> +{
>> >> +     spin_lock(&vport->stats_lock);
>> >
>> > Sorry for over analyzing this... but I don't think the stats_lock
>> > is necessary either. The only thing it is protecting is against 64 bit
>> > wrap. If you used another u64_stat_sync for that one, it could be eliminated.
>> >
>> > Maybe?
>>
>> The reason for stats_lock is that the error stats are not expected to
>> be contended so in order to save some memory they're not per-cpu and
>> we just use a spin lock to protect them.
>
> Assignment or increment of native type size (64 bit on 64 bit cpu)
> is always atomic.

It might be, but it not always is. For example, on load-store
architectures normal increment (load,inc,store) is not atomic unless
made with special instruction sequence (like LDR/STREX on ARM).

Best Regards,
Michał Mirosław
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Patch

--- a/net/openvswitch/vport.c	2011-11-21 13:56:54.991757053 -0800
+++ b/net/openvswitch/vport.c	2011-11-21 13:57:49.352333329 -0800
@@ -130,8 +130,6 @@  struct vport *vport_alloc(int priv_size,
 	if (!vport->percpu_stats)
 		return ERR_PTR(-ENOMEM);
 
-	spin_lock_init(&vport->stats_lock);
-
 	return vport;
 }
 
@@ -235,6 +233,7 @@  void vport_del(struct vport *vport)
 void vport_get_stats(struct vport *vport, struct ovs_vport_stats *stats)
 {
 	int i;
+	unsigned int start;
 
 	memset(stats, 0, sizeof(*stats));
 
@@ -247,19 +246,17 @@  void vport_get_stats(struct vport *vport
 	 * netdev-stats can be directly read over netlink-ioctl.
 	 */
 
-	spin_lock_bh(&vport->stats_lock);
-
-	stats->rx_errors	= vport->err_stats.rx_errors;
-	stats->tx_errors	= vport->err_stats.tx_errors;
-	stats->tx_dropped	= vport->err_stats.tx_dropped;
-	stats->rx_dropped	= vport->err_stats.rx_dropped;
-
-	spin_unlock_bh(&vport->stats_lock);
+	do {
+		start = u64_stats_fetch_begin_bh(&vport->err_stats.sync);
+		stats->rx_errors	= vport->err_stats.rx_errors;
+		stats->tx_errors	= vport->err_stats.tx_errors;
+		stats->tx_dropped	= vport->err_stats.tx_dropped;
+		stats->rx_dropped	= vport->err_stats.rx_dropped;
+	} while (u64_stats_fetch_retry_bh(&vport->err_stats.sync, start));
 
 	for_each_possible_cpu(i) {
 		const struct vport_percpu_stats *percpu_stats;
 		struct vport_percpu_stats local_stats;
-		unsigned int start;
 
 		percpu_stats = per_cpu_ptr(vport->percpu_stats, i);
 
@@ -372,7 +369,7 @@  int vport_send(struct vport *vport, stru
  */
 void vport_record_error(struct vport *vport, enum vport_err_type err_type)
 {
-	spin_lock(&vport->stats_lock);
+	u64_stats_update_begin(&vport->err_stats.sync);
 
 	switch (err_type) {
 	case VPORT_E_RX_DROPPED:
@@ -392,5 +389,5 @@  void vport_record_error(struct vport *vp
 		break;
 	};
 
-	spin_unlock(&vport->stats_lock);
+	u64_stats_update_end(&vport->err_stats.sync);
 }
--- a/net/openvswitch/vport.h	2011-11-21 13:56:54.991757053 -0800
+++ b/net/openvswitch/vport.h	2011-11-21 13:58:01.448461585 -0800
@@ -62,6 +62,7 @@  struct vport_err_stats {
 	u64 rx_errors;
 	u64 tx_dropped;
 	u64 tx_errors;
+	struct u64_stats_sync sync;
 };
 
 /**