[patch 4/5] net: hip04: Make tx coalesce timer actually work

[patch 4/5] net: hip04: Make tx coalesce timer actually work

[Thomas Gleixner]

[-- Attachment #1: net-hip04-fix-hrtimer-wreckage.patch --]
[-- Type: text/plain, Size: 2869 bytes --]

The code sets the expiry value of the timer to a relative value and
starts it with hrtimer_start_expires. That's fine, but that only works
once. The timer is started in relative mode, so the expiry value gets
overwritten with the absolut expiry time (now + expiry).

So once the timer expired, a new call to hrtimer_start_expires results
in an immidiately expired timer, because the expiry value is
already in the past.

Use the proper mechanisms to (re)start the timer in the intended way.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: dingtianhong <dingtianhong@huawei.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: netdev@vger.kernel.org
---
 drivers/net/ethernet/hisilicon/hip04_eth.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

Index: linux/drivers/net/ethernet/hisilicon/hip04_eth.c
===================================================================
--- linux.orig/drivers/net/ethernet/hisilicon/hip04_eth.c
+++ linux/drivers/net/ethernet/hisilicon/hip04_eth.c
@@ -413,6 +413,15 @@ out:
 	return count;
 }
 
+static void hip04_start_tx_timer(struct hip04_priv *priv)
+{
+	ktime_t t;
+
+	/* allow timer to fire after half the time at the earliest */
+	t = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
+	hrtimer_start(&priv->tx_coalesce_timer, t, HRTIMER_MODE_REL);
+}
+
 static int hip04_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct hip04_priv *priv = netdev_priv(ndev);
@@ -466,8 +475,7 @@ static int hip04_mac_start_xmit(struct s
 		}
 	} else if (!hrtimer_is_queued(&priv->tx_coalesce_timer)) {
 		/* cleanup not pending yet, start a new timer */
-		hrtimer_start_expires(&priv->tx_coalesce_timer,
-				      HRTIMER_MODE_REL);
+		hip04_start_tx_timer(priv);
 	}
 
 	return NETDEV_TX_OK;
@@ -549,7 +557,7 @@ done:
 	/* clean up tx descriptors and start a new timer if necessary */
 	tx_remaining = hip04_tx_reclaim(ndev, false);
 	if (rx < budget && tx_remaining)
-		hrtimer_start_expires(&priv->tx_coalesce_timer, HRTIMER_MODE_REL);
+		hip04_start_tx_timer(priv);
 
 	return rx;
 }
@@ -809,7 +817,6 @@ static int hip04_mac_probe(struct platfo
 	struct hip04_priv *priv;
 	struct resource *res;
 	unsigned int irq;
-	ktime_t txtime;
 	int ret;
 
 	ndev = alloc_etherdev(sizeof(struct hip04_priv));
@@ -846,9 +853,6 @@ static int hip04_mac_probe(struct platfo
 	 */
 	priv->tx_coalesce_frames = TX_DESC_NUM * 3 / 4;
 	priv->tx_coalesce_usecs = 200;
-	/* allow timer to fire after half the time at the earliest */
-	txtime = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
-	hrtimer_set_expires_range(&priv->tx_coalesce_timer, txtime, txtime);
 	priv->tx_coalesce_timer.function = tx_done;
 
 	priv->map = syscon_node_to_regmap(arg.np);

Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

[Arnd Bergmann]

On Monday 13 April 2015 21:02:23 Thomas Gleixner wrote:
> The code sets the expiry value of the timer to a relative value and
> starts it with hrtimer_start_expires. That's fine, but that only works
> once. The timer is started in relative mode, so the expiry value gets
> overwritten with the absolut expiry time (now + expiry).
> 
> So once the timer expired, a new call to hrtimer_start_expires results
> in an immidiately expired timer, because the expiry value is
> already in the past.
> 
> Use the proper mechanisms to (re)start the timer in the intended way.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: dingtianhong <dingtianhong@huawei.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: netdev@vger.kernel.org

Thanks a lot for the fix. The mistake was clearly mine, as I had sent
a patch to introduce the tx coalesce timer without access to hardware
or a way to test that what I did was correct.

There are other known problems in the version of the driver that got
merged, and I believe that someone is now looking at them.

What I think we really want here is a way for user space to configure
both the minimum and maximum coalesce timer separately rather than
assuming half the time is what we want.

	Arnd

> @@ -413,6 +413,15 @@ out:
>  	return count;
>  }
>  
> +static void hip04_start_tx_timer(struct hip04_priv *priv)
> +{
> +	ktime_t t;
> +
> +	/* allow timer to fire after half the time at the earliest */
> +	t = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
> +	hrtimer_start(&priv->tx_coalesce_timer, t, HRTIMER_MODE_REL);
> +}

Question: this looks to me like it sets both the minimum and maximum
time to priv->tx_coalesce_usecs/2, when the intention was to set
the minimum to priv->tx_coalesce_usecs/2 and the maximum to
priv->tx_coalesce_usecs. Am I missing something subtle here, or did
you just misread my original intention from the botched code?

	Arnd

Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

[Thomas Gleixner]

On Mon, 13 Apr 2015, Arnd Bergmann wrote:

> On Monday 13 April 2015 21:02:23 Thomas Gleixner wrote:
> > The code sets the expiry value of the timer to a relative value and
> > starts it with hrtimer_start_expires. That's fine, but that only works
> > once. The timer is started in relative mode, so the expiry value gets
> > overwritten with the absolut expiry time (now + expiry).
> > 
> > So once the timer expired, a new call to hrtimer_start_expires results
> > in an immidiately expired timer, because the expiry value is
> > already in the past.
> > 
> > Use the proper mechanisms to (re)start the timer in the intended way.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > Cc: dingtianhong <dingtianhong@huawei.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
> > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > Cc: netdev@vger.kernel.org
> 
> Thanks a lot for the fix. The mistake was clearly mine, as I had sent
> a patch to introduce the tx coalesce timer without access to hardware
> or a way to test that what I did was correct.
> 
> There are other known problems in the version of the driver that got
> merged, and I believe that someone is now looking at them.
> 
> What I think we really want here is a way for user space to configure
> both the minimum and maximum coalesce timer separately rather than
> assuming half the time is what we want.
> 
> 	Arnd
> 
> > @@ -413,6 +413,15 @@ out:
> >  	return count;
> >  }
> >  
> > +static void hip04_start_tx_timer(struct hip04_priv *priv)
> > +{
> > +	ktime_t t;
> > +
> > +	/* allow timer to fire after half the time at the earliest */
> > +	t = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
> > +	hrtimer_start(&priv->tx_coalesce_timer, t, HRTIMER_MODE_REL);
> > +}
> 
> Question: this looks to me like it sets both the minimum and maximum
> time to priv->tx_coalesce_usecs/2, when the intention was to set
> the minimum to priv->tx_coalesce_usecs/2 and the maximum to
> priv->tx_coalesce_usecs. Am I missing something subtle here, or did
> you just misread my original intention from the botched code?

Yes, I missed that. Simple fix for this is:

  unsigned long t_ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
  
  hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(t_ns),
			 t_ns, HRTIMER_MODE_REL);

Thanks,

	tglx

Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

[Arnd Bergmann]

On Monday 13 April 2015 23:42:03 Thomas Gleixner wrote:
> > 
> > Question: this looks to me like it sets both the minimum and maximum
> > time to priv->tx_coalesce_usecs/2, when the intention was to set
> > the minimum to priv->tx_coalesce_usecs/2 and the maximum to
> > priv->tx_coalesce_usecs. Am I missing something subtle here, or did
> > you just misread my original intention from the botched code?
> 
> Yes, I missed that. Simple fix for this is:
> 
>   unsigned long t_ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
>   
>   hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(t_ns),
>                          t_ns, HRTIMER_MODE_REL);

Ah, good. I have to admit that I'd probably make the same mistake
again if I was to do this for another driver and you hadn't sent
the fix. The hrtimer_set_expires_range() function just looked like
it had been designed for the use case I was interested in ;-).

Any idea how to prevent the next person from making the same mistake?

	Arnd

Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

[Thomas Gleixner]

On Tue, 14 Apr 2015, Arnd Bergmann wrote:
> On Monday 13 April 2015 23:42:03 Thomas Gleixner wrote:
> > > 
> > > Question: this looks to me like it sets both the minimum and maximum
> > > time to priv->tx_coalesce_usecs/2, when the intention was to set
> > > the minimum to priv->tx_coalesce_usecs/2 and the maximum to
> > > priv->tx_coalesce_usecs. Am I missing something subtle here, or did
> > > you just misread my original intention from the botched code?
> > 
> > Yes, I missed that. Simple fix for this is:
> > 
> >   unsigned long t_ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
> >   
> >   hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(t_ns),
> >                          t_ns, HRTIMER_MODE_REL);
> 
> Ah, good. I have to admit that I'd probably make the same mistake
> again if I was to do this for another driver and you hadn't sent
> the fix. The hrtimer_set_expires_range() function just looked like
> it had been designed for the use case I was interested in ;-).
> 
> Any idea how to prevent the next person from making the same mistake?

Yes. Documentation :)

Thanks,

	tglx

Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

[Ding Tianhong]

On 2015/4/14 6:08, Thomas Gleixner wrote:
> On Tue, 14 Apr 2015, Arnd Bergmann wrote:
>> On Monday 13 April 2015 23:42:03 Thomas Gleixner wrote:
>>>>
>>>> Question: this looks to me like it sets both the minimum and maximum
>>>> time to priv->tx_coalesce_usecs/2, when the intention was to set
>>>> the minimum to priv->tx_coalesce_usecs/2 and the maximum to
>>>> priv->tx_coalesce_usecs. Am I missing something subtle here, or did
>>>> you just misread my original intention from the botched code?
>>>
>>> Yes, I missed that. Simple fix for this is:
>>>
>>>   unsigned long t_ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
>>>   
>>>   hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(t_ns),
>>>                          t_ns, HRTIMER_MODE_REL);
>>
>> Ah, good. I have to admit that I'd probably make the same mistake
>> again if I was to do this for another driver and you hadn't sent
>> the fix. The hrtimer_set_expires_range() function just looked like
>> it had been designed for the use case I was interested in ;-).
>>
>> Any idea how to prevent the next person from making the same mistake?
> 
> Yes. Documentation :)
> 
Looks good to me, thanks everyone.

Ding

> Thanks,
> 
> 	tglx
> 
> .
> 

Re: [patch 4/5] net: hip04: Make tx coalesce timer actually work

[David Miller]

From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 14 Apr 2015 00:08:23 +0200 (CEST)

> On Tue, 14 Apr 2015, Arnd Bergmann wrote:
>> On Monday 13 April 2015 23:42:03 Thomas Gleixner wrote:
>> > > 
>> > > Question: this looks to me like it sets both the minimum and maximum
>> > > time to priv->tx_coalesce_usecs/2, when the intention was to set
>> > > the minimum to priv->tx_coalesce_usecs/2 and the maximum to
>> > > priv->tx_coalesce_usecs. Am I missing something subtle here, or did
>> > > you just misread my original intention from the botched code?
>> > 
>> > Yes, I missed that. Simple fix for this is:
>> > 
>> >   unsigned long t_ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
>> >   
>> >   hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(t_ns),
>> >                          t_ns, HRTIMER_MODE_REL);
>> 
>> Ah, good. I have to admit that I'd probably make the same mistake
>> again if I was to do this for another driver and you hadn't sent
>> the fix. The hrtimer_set_expires_range() function just looked like
>> it had been designed for the use case I was interested in ;-).
>> 
>> Any idea how to prevent the next person from making the same mistake?
> 
> Yes. Documentation :)

Can I get a respin of this patch with the above?

[patch v2] net: hip04: Make tx coalesce timer actually work

[Thomas Gleixner]

The code sets the expiry value of the timer to a relative value and
starts it with hrtimer_start_expires. That's fine, but that only works
once. The timer is started in relative mode, so the expiry value gets
overwritten with the absolut expiry time (now + expiry).

So once the timer expired, a new call to hrtimer_start_expires results
in an immidiately expired timer, because the expiry value is
already in the past.

Use the proper mechanisms to (re)start the timer in the intended way.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: dingtianhong <dingtianhong@huawei.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: netdev@vger.kernel.org
---
 drivers/net/ethernet/hisilicon/hip04_eth.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

Index: linux/drivers/net/ethernet/hisilicon/hip04_eth.c
===================================================================
--- linux.orig/drivers/net/ethernet/hisilicon/hip04_eth.c
+++ linux/drivers/net/ethernet/hisilicon/hip04_eth.c
@@ -413,6 +413,15 @@ out:
 	return count;
 }
 
+static void hip04_start_tx_timer(struct hip04_priv *priv)
+{
+	unsigned long ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
+
+	/* allow timer to fire after half the time at the earliest */
+	hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(ns),
+			       ns, HRTIMER_MODE_REL);
+}
+
 static int hip04_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct hip04_priv *priv = netdev_priv(ndev);
@@ -466,8 +475,7 @@ static int hip04_mac_start_xmit(struct s
 		}
 	} else if (!hrtimer_is_queued(&priv->tx_coalesce_timer)) {
 		/* cleanup not pending yet, start a new timer */
-		hrtimer_start_expires(&priv->tx_coalesce_timer,
-				      HRTIMER_MODE_REL);
+		hip04_start_tx_timer(priv);
 	}
 
 	return NETDEV_TX_OK;
@@ -549,7 +557,7 @@ done:
 	/* clean up tx descriptors and start a new timer if necessary */
 	tx_remaining = hip04_tx_reclaim(ndev, false);
 	if (rx < budget && tx_remaining)
-		hrtimer_start_expires(&priv->tx_coalesce_timer, HRTIMER_MODE_REL);
+		hip04_start_tx_timer(priv);
 
 	return rx;
 }
@@ -809,7 +817,6 @@ static int hip04_mac_probe(struct platfo
 	struct hip04_priv *priv;
 	struct resource *res;
 	unsigned int irq;
-	ktime_t txtime;
 	int ret;
 
 	ndev = alloc_etherdev(sizeof(struct hip04_priv));
@@ -846,9 +853,6 @@ static int hip04_mac_probe(struct platfo
 	 */
 	priv->tx_coalesce_frames = TX_DESC_NUM * 3 / 4;
 	priv->tx_coalesce_usecs = 200;
-	/* allow timer to fire after half the time at the earliest */
-	txtime = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
-	hrtimer_set_expires_range(&priv->tx_coalesce_timer, txtime, txtime);
 	priv->tx_coalesce_timer.function = tx_done;
 
 	priv->map = syscon_node_to_regmap(arg.np);

Re: [patch v2] net: hip04: Make tx coalesce timer actually work

[Ding Tianhong]

On 2015/4/15 3:42, Thomas Gleixner wrote:
> The code sets the expiry value of the timer to a relative value and
> starts it with hrtimer_start_expires. That's fine, but that only works
> once. The timer is started in relative mode, so the expiry value gets
> overwritten with the absolut expiry time (now + expiry).
> 
> So once the timer expired, a new call to hrtimer_start_expires results
> in an immidiately expired timer, because the expiry value is
> already in the past.
> 
> Use the proper mechanisms to (re)start the timer in the intended way.
> 

Acked-by: Ding Tianhong <dingtianhong@huawei.com>

> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: dingtianhong <dingtianhong@huawei.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: netdev@vger.kernel.org
> ---
>  drivers/net/ethernet/hisilicon/hip04_eth.c |   18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> Index: linux/drivers/net/ethernet/hisilicon/hip04_eth.c
> ===================================================================
> --- linux.orig/drivers/net/ethernet/hisilicon/hip04_eth.c
> +++ linux/drivers/net/ethernet/hisilicon/hip04_eth.c
> @@ -413,6 +413,15 @@ out:
>  	return count;
>  }
>  
> +static void hip04_start_tx_timer(struct hip04_priv *priv)
> +{
> +	unsigned long ns = priv->tx_coalesce_usecs * NSEC_PER_USEC / 2;
> +
> +	/* allow timer to fire after half the time at the earliest */
> +	hrtimer_start_range_ns(&priv->tx_coalesce_timer, ns_to_ktime(ns),
> +			       ns, HRTIMER_MODE_REL);
> +}
> +
>  static int hip04_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  {
>  	struct hip04_priv *priv = netdev_priv(ndev);
> @@ -466,8 +475,7 @@ static int hip04_mac_start_xmit(struct s
>  		}
>  	} else if (!hrtimer_is_queued(&priv->tx_coalesce_timer)) {
>  		/* cleanup not pending yet, start a new timer */
> -		hrtimer_start_expires(&priv->tx_coalesce_timer,
> -				      HRTIMER_MODE_REL);
> +		hip04_start_tx_timer(priv);
>  	}
>  
>  	return NETDEV_TX_OK;
> @@ -549,7 +557,7 @@ done:
>  	/* clean up tx descriptors and start a new timer if necessary */
>  	tx_remaining = hip04_tx_reclaim(ndev, false);
>  	if (rx < budget && tx_remaining)
> -		hrtimer_start_expires(&priv->tx_coalesce_timer, HRTIMER_MODE_REL);
> +		hip04_start_tx_timer(priv);
>  
>  	return rx;
>  }
> @@ -809,7 +817,6 @@ static int hip04_mac_probe(struct platfo
>  	struct hip04_priv *priv;
>  	struct resource *res;
>  	unsigned int irq;
> -	ktime_t txtime;
>  	int ret;
>  
>  	ndev = alloc_etherdev(sizeof(struct hip04_priv));
> @@ -846,9 +853,6 @@ static int hip04_mac_probe(struct platfo
>  	 */
>  	priv->tx_coalesce_frames = TX_DESC_NUM * 3 / 4;
>  	priv->tx_coalesce_usecs = 200;
> -	/* allow timer to fire after half the time at the earliest */
> -	txtime = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
> -	hrtimer_set_expires_range(&priv->tx_coalesce_timer, txtime, txtime);
>  	priv->tx_coalesce_timer.function = tx_done;
>  
>  	priv->map = syscon_node_to_regmap(arg.np);
> 
> .
> 

Re: [patch v2] net: hip04: Make tx coalesce timer actually work

[Arnd Bergmann]

On Tuesday 14 April 2015 21:42:42 Thomas Gleixner wrote:
> The code sets the expiry value of the timer to a relative value and
> starts it with hrtimer_start_expires. That's fine, but that only works
> once. The timer is started in relative mode, so the expiry value gets
> overwritten with the absolut expiry time (now + expiry).
> 
> So once the timer expired, a new call to hrtimer_start_expires results
> in an immidiately expired timer, because the expiry value is
> already in the past.
> 
> Use the proper mechanisms to (re)start the timer in the intended way.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: dingtianhong <dingtianhong@huawei.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Zhangfei Gao <zhangfei.gao@linaro.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: netdev@vger.kernel.org
> 

Acked-by: Arnd Bergmann <arnd@arndb.de>

Re: [patch v2] net: hip04: Make tx coalesce timer actually work

[David Miller]

From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 14 Apr 2015 21:42:42 +0200 (CEST)

> The code sets the expiry value of the timer to a relative value and
> starts it with hrtimer_start_expires. That's fine, but that only works
> once. The timer is started in relative mode, so the expiry value gets
> overwritten with the absolut expiry time (now + expiry).
> 
> So once the timer expired, a new call to hrtimer_start_expires results
> in an immidiately expired timer, because the expiry value is
> already in the past.
> 
> Use the proper mechanisms to (re)start the timer in the intended way.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Applied, thanks Thomas.