netdev - Re: [PATCH] forcedeth: msi interrupts

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Message-Id: <20080604151854.4a6f22b8.akpm@linux-foundation.org>
Date:	Wed, 4 Jun 2008 15:18:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ayaz Abdulla <aabdulla@...dia.com>
Cc:	jgarzik@...ox.com, manfred@...orfullife.com,
	akpm@...uxfoundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH] forcedeth: msi interrupts

On Tue, 03 Jun 2008 16:51:46 -0400
Ayaz Abdulla <aabdulla@...dia.com> wrote:

> This patch adds a workaround for lost MSI interrupts. There is a race 
> condition in the HW in which future interrupts could be missed. The 
> workaround is to toggle the MSI irq mask.
> 

Do you think this is a 2.6.26 thing?

> [patch-forcedeth-msi-irq  text/plain (1.3KB)]
> --- old/drivers/net/forcedeth.c	2008-06-03 16:16:26.000000000 -0400
> +++ new/drivers/net/forcedeth.c	2008-06-03 16:31:44.000000000 -0400
> @@ -3277,6 +3277,20 @@
>  	dprintk(KERN_DEBUG "%s: link change notification done.\n", dev->name);
>  }
>  
> +static inline void nv_msi_workaround(struct net_device *dev)
> +{
> +	struct fe_priv *np = netdev_priv(dev);
> +	u8 __iomem *base = get_hwbase(dev);
> +
> +	/* Need to toggle the msi irq mask within the ethernet device,
> +	 * otherwise, future interrupts will not be detected.
> +	 */
> +	if (np->msi_flags & NV_MSI_ENABLED) {
> +		writel(0, base + NvRegMSIIrqMask);
> +		writel(NVREG_MSI_VECTOR_0_ENABLED, base + NvRegMSIIrqMask);
> +	}
> +}
> +
>  static irqreturn_t nv_nic_irq(int foo, void *data)
>  {
>  	struct net_device *dev = (struct net_device *) data;
> @@ -3299,6 +3313,8 @@
>  		if (!(events & np->irqmask))
>  			break;
>  
> +		nv_msi_workaround(dev);
> +
>  		spin_lock(&np->lock);
>  		nv_tx_done(dev);
>  		spin_unlock(&np->lock);
> @@ -3414,6 +3430,8 @@
>  		if (!(events & np->irqmask))
>  			break;
>  
> +		nv_msi_workaround(dev);
> +
>  		spin_lock(&np->lock);
>  		nv_tx_done_optimized(dev, TX_WORK_PER_LOOP);
>  		spin_unlock(&np->lock);
> @@ -3754,6 +3772,8 @@
>  	if (!(events & NVREG_IRQ_TIMER))
>  		return IRQ_RETVAL(0);
>  
> +	nv_msi_workaround(dev);
> +
>  	spin_lock(&np->lock);
>  	np->intr_test = 1;
>  	spin_unlock(&np->lock);
> 

I'm not loving the implementation.

- That `inline' adds 35 bytes more text to the driver, and we expect
  that this often yields slower code.

- Every caller of nv_msi_workaround() already has the fe_priv* in a
  local variable, so why not pass that in and save the additional
  pointer calculation?

So this:

diff -puN drivers/net/forcedeth.c~forcedeth-msi-interrupts-uninlining drivers/net/forcedeth.c
--- a/drivers/net/forcedeth.c~forcedeth-msi-interrupts-uninlining
+++ a/drivers/net/forcedeth.c
@@ -3277,15 +3277,14 @@ static void nv_link_irq(struct net_devic
 	dprintk(KERN_DEBUG "%s: link change notification done.\n", dev->name);
 }
 
-static inline void nv_msi_workaround(struct net_device *dev)
+static void nv_msi_workaround(struct fe_priv *np)
 {
-	struct fe_priv *np = netdev_priv(dev);
-	u8 __iomem *base = get_hwbase(dev);
-
 	/* Need to toggle the msi irq mask within the ethernet device,
 	 * otherwise, future interrupts will not be detected.
 	 */
 	if (np->msi_flags & NV_MSI_ENABLED) {
+		u8 __iomem *base = np->base;
+
 		writel(0, base + NvRegMSIIrqMask);
 		writel(NVREG_MSI_VECTOR_0_ENABLED, base + NvRegMSIIrqMask);
 	}
@@ -3313,7 +3312,7 @@ static irqreturn_t nv_nic_irq(int foo, v
 		if (!(events & np->irqmask))
 			break;
 
-		nv_msi_workaround(dev);
+		nv_msi_workaround(np);
 
 		spin_lock(&np->lock);
 		nv_tx_done(dev);
@@ -3430,7 +3429,7 @@ static irqreturn_t nv_nic_irq_optimized(
 		if (!(events & np->irqmask))
 			break;
 
-		nv_msi_workaround(dev);
+		nv_msi_workaround(np);
 
 		spin_lock(&np->lock);
 		nv_tx_done_optimized(dev, TX_WORK_PER_LOOP);
@@ -3772,7 +3771,7 @@ static irqreturn_t nv_nic_irq_test(int f
 	if (!(events & NVREG_IRQ_TIMER))
 		return IRQ_RETVAL(0);
 
-	nv_msi_workaround(dev);
+	nv_msi_workaround(np);
 
 	spin_lock(&np->lock);
 	np->intr_test = 1;
_


save 42 bytes of text.

Now, if the (np->msi_flags & NV_MSI_ENABLED) test is usually false then
there might be some advantage in inlining the whole thing.  Or just
inlining the NV_MSI_ENABLED test, but those two writel()s probably
aren't worth the fuss of uninlining.



Semi-relatedly, the driver does an awful lot of this:

	struct fe_priv *np = get_nvpriv(dev);
	u8 __iomem *base = get_hwbase(dev);

but get_hwbase() re-evaluates netdev_priv().  It would be more
efficient to pass an fe_priv* into get_hwbase().  Or, better, just
remove get_hwbase() and open-code `np->base' everywhere.



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