linux-kernel - Re: [PATCH 9/9] PCI: only enable pci realloc when SRIOV bar is not assigned

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Message-ID: <20120210130029.44d2a823@jbarnes-desktop>
Date:	Fri, 10 Feb 2012 13:00:29 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ram Pai <linuxram@...ibm.com>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] PCI: only enable pci realloc when SRIOV bar is not
 assigned

On Sat,  4 Feb 2012 22:55:08 -0800
Yinghai Lu <yinghai@...nel.org> wrote:

> If bios does not assign those BAR or wrong address, then kernel will
> try to do pci realloc.
> 
> in that case, user still can use pci=realloc=off to override it.
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> ---
>  drivers/pci/setup-bus.c |   28 ++++++++++++++++++++++++++++
>  1 files changed, 28 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 9526038..520f256 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -1293,6 +1293,31 @@ static bool __init pci_realloc_enabled(void)
>  	return pci_realloc_enable >= enable_yes_user;
>  }
>  
> +static void __init pci_realloc_detect(void)
> +{
> +	struct pci_dev *dev = NULL;
> +
> +	if (pci_realloc_enable != enable_not_set)
> +		return;
> +
> +#ifdef CONFIG_PCI_IOV
> +	for_each_pci_dev(dev) {
> +		int i;
> +
> +		for (i = PCI_IOV_RESOURCES; i <= PCI_IOV_RESOURCE_END; i++) {
> +			struct resource *r = &dev->resource[i];
> +
> +			/* Not assigned, or rejected by kernel */
> +			if (r->flags && !r->start) {
> +				pci_realloc_enable = enable_yes_detected;
> +
> +				return;
> +			}
> +		}
> +	}
> +#endif
> +}
> +
>  /*
>   * first try will not touch pci bridge res
>   * second  and later try will clear small leaf bridge res
> @@ -1314,6 +1339,7 @@ pci_assign_unassigned_resources(void)
>  	int pci_try_num = 1;
>  
>  	/* don't realloc if asked to do so */
> +	pci_realloc_detect();
>  	if (pci_realloc_enabled()) {
>  		int max_depth = pci_get_max_depth();
>  
> @@ -1348,6 +1374,8 @@ again:
>  	if (tried_times >= pci_try_num) {
>  		if (pci_realloc_enable == enable_not_set)
>  			printk(KERN_INFO "Some pci devices resources are not assigned, please try to boot with pci=realloc\n");
> +		else if (pci_realloc_enable == enable_yes_detected)
> +			printk(KERN_INFO "Automatically enabled pci realloc, if you have problem, please try to boot with pci=realloc=off\n");
>  
>  		free_list(&fail_head);
>  		goto enable_and_dump;

Not sure I like this one either.  Distros will want to enable IOV by
default, but in most configs users still won't use it, and many BIOSes
won't bother to allocate IOV space.  So defaulting to trying to do so
will likely cause a lot of unnecessary re-allocation.

So distro guidance would be appreciated here for the default behavior.
-- 
Jesse Barnes, Intel Open Source Technology Center

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