linux-kernel - RE: [PATCH RFC v2 29/29] vmxnet3: Make use of pcim_enable_msix

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Date:	Mon, 21 Oct 2013 09:51:32 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Alexander Gordeev" <agordeev@...hat.com>,
	<linux-kernel@...r.kernel.org>
Cc:	"Bjorn Helgaas" <bhelgaas@...gle.com>,
	"Michael Ellerman" <michael@...erman.id.au>,
	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
	"Tejun Heo" <tj@...nel.org>,
	"Ben Hutchings" <bhutchings@...arflare.com>,
	"Mark Lord" <kernel@...rt.ca>, "H. Peter Anvin" <hpa@...or.com>,
	<linux-pci@...r.kernel.org>
Subject: RE: [PATCH RFC v2 29/29] vmxnet3: Make use of pcim_enable_msix_range() interface

> Subject: [PATCH RFC v2 29/29] vmxnet3: Make use of pcim_enable_msix_range() interface
...
> diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
> index d33802c..e552d2b 100644
> --- a/drivers/net/vmxnet3/vmxnet3_drv.c
> +++ b/drivers/net/vmxnet3/vmxnet3_drv.c
> @@ -2735,39 +2735,19 @@ vmxnet3_read_mac_addr(struct vmxnet3_adapter *adapter, u8 *mac)
>   */
> 
>  static int
> -vmxnet3_acquire_msix_vectors(struct vmxnet3_adapter *adapter,
> -			     int vectors)
> +vmxnet3_acquire_msix_vectors(struct vmxnet3_adapter *adapter, int vectors)
>  {
> -	int err = -EINVAL, vector_threshold;
> -	vector_threshold = VMXNET3_LINUX_MIN_MSIX_VECT;
> -
> -	while (vectors >= vector_threshold) {
> -		err = pci_enable_msix(adapter->pdev, adapter->intr.msix_entries,
> -				      vectors);
> -		if (!err) {
> -			adapter->intr.num_intrs = vectors;
> -			return 0;
> -		} else if (err < 0) {
> -			dev_err(&adapter->netdev->dev,
> -				   "Failed to enable MSI-X, error: %d\n", err);
> -			return err;
> -		} else if (err < vector_threshold) {
> -			dev_info(&adapter->pdev->dev,
> -				 "Number of MSI-Xs which can be allocated "
> -				 "is lower than min threshold required.\n");
> -			return -ENOSPC;
> -		} else {
> -			/* If fails to enable required number of MSI-x vectors
> -			 * try enabling minimum number of vectors required.
> -			 */
> -			dev_err(&adapter->netdev->dev,
> -				"Failed to enable %d MSI-X, trying %d instead\n",
> -				    vectors, vector_threshold);
> -			vectors = vector_threshold;
> -		}
> +	vectors = pcim_enable_msix_range(adapter->pdev,
> +					 adapter->intr.msix_entries, vectors,
> +					 VMXNET3_LINUX_MIN_MSIX_VECT);
> +	if (vectors < 0) {
> +		dev_err(&adapter->netdev->dev,
> +			"Failed to enable MSI-X, error: %d\n", vectors);
> +		return vectors;
>  	}
> 
> -	return err;
> +	adapter->intr.num_intrs = vectors;
> +	return 0;
>  }

AFAICT the old code either used the requested number or the minimum number.
The new code seems to claim an intermediate number of interrupts - but probably
only uses the minimum number.
This wastes the last few MSI-X interrupts.
The code (especially the calling code) would be easier to read if the 'vectors'
value wasn't explicitly passed.

	David



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