linux-kernel - Re: [PATCH] msi-x: let drivers retry when not enough vectors

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Date:	Thu, 07 May 2009 13:44:38 +0300
From:	Avi Kivity <avi@...hat.com>
To:	michael@...erman.id.au
CC:	Matthew Wilcox <matthew@....cx>,
	Sheng Yang <sheng@...ux.intel.com>, kvm@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>, jbarnes@...tuousgeek.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] msi-x: let drivers retry when not enough vectors

Michael Ellerman wrote:
> Not to mention that there's no guarantee that you'll get as many
> interrupts as the device supports, so you should really be coding to
> cope with that anyway. Like the example in MSI-HOWTO.txt:
>
> 197 static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)
> 198 {
> 199         while (nvec >= FOO_DRIVER_MINIMUM_NVEC) {
> 200                 rc = pci_enable_msix(adapter->pdev,
> 201                                      adapter->msix_entries, nvec);
> 202                 if (rc > 0)
> 203                         nvec = rc;
> 204                 else
> 205                         return rc;
> 206         }
> 207 
> 208         return -ENOSPC;
> 209 }
>
> So I agree, this patch is an improvement.
>   

I imagine this loop is present in many drivers.  So why not add a helper

static int pci_enable_msix_min(struct foo_adapter *adapter, int min_nvec)
{
	int nvec = 2048;

        while (nvec >= min_nvec) {
                rc = pci_enable_msix(adapter->pdev,
                                     adapter->msix_entries, nvec);
                if (rc == 0)
                        return nvec;
                else if (rc > 0)
                        nvec = rc;
                else
                        return rc;
        }
        return -ENOSPC;
}



-- 
error compiling committee.c: too many arguments to function

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