netdev - Re: [PATCH v2] netpoll: Introduce netpoll_carrier

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Message-ID: <20090708105902.GB6000@hmsreliant.think-freely.org>
Date:	Wed, 8 Jul 2009 06:59:02 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] netpoll: Introduce netpoll_carrier_timeout kernel
	option

On Wed, Jul 08, 2009 at 05:30:11AM +0400, Anton Vorontsov wrote:
> Some PHYs require longer timeouts for carrier detection, and
> auto-negotiation process may take indefinite amount of time.
> 
> It may be inconvenient to force longer timeouts for sane PHYs,
> so let's introduce a kernel command line option.
> 
> Since we're using module_param(), the option also can be
> changed in runtime.
> 
> Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>
> ---
> 
> On Tue, Jul 07, 2009 at 06:03:54PM -0700, Stephen Hemminger wrote:
> > On Wed, 8 Jul 2009 05:00:30 +0400
> > Anton Vorontsov <avorontsov@...mvista.com> wrote:
> > 
> > > Some PHYs require longer timeouts for carrier detection, and
> > > auto-negotiation process may take indefinite amount of time.
> > > 
> > > It may be inconvenient to force longer timeouts for sane PHYs,
> > > so let's introduce a kernel command line option.
> > > 
> > > Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>
> > > ---
> > >  Documentation/kernel-parameters.txt |    5 +++++
> > >  net/core/netpoll.c                  |   11 ++++++++++-
> > >  2 files changed, 15 insertions(+), 1 deletions(-)
> > 
> > A sysctl (or module option) is a less awkward interface for something
> > like this.
> 
> Right you are, and it's less code. Wasn't sure if it makes sense
> to use module_param() for non-modular code, but afterall it makes
> sense indeed, since with it we can change the timeout in runtime.
> 
> > Kernel command line parameters are ugly step children
> > loved only by embedded developers.
> 
> So true! ;-)
> 
> How about this patch?
> 
> Thanks,
> 
>  Documentation/kernel-parameters.txt |    5 +++++
>  net/core/netpoll.c                  |    6 +++++-
>  2 files changed, 10 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index d77fbd8..9347f4a 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1531,6 +1531,11 @@ and is between 256 and 4096 characters. It is defined in the file
>  			symbolic names: lapic and ioapic
>  			Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
>  
> +	netpoll.carrier_timeout=
> +			[NET] Specifies amount of time (in seconds) that
> +			netpoll should wait for a carrier. By default netpoll
> +			waits 4 seconds.
> +
I'm not sure the documentation still belongs in kernel-parameters.txt if you
make this a module options, but thats just a nit.



>  
> +#include <linux/moduleparam.h>
>  #include <linux/netdevice.h>
>  #include <linux/etherdevice.h>
>  #include <linux/string.h>
> @@ -50,6 +51,9 @@ static atomic_t trapped;
>  static void zap_completion_queue(void);
>  static void arp_reply(struct sk_buff *skb);
>  
> +static unsigned int carrier_timeout = 4;
> +module_param(carrier_timeout, uint, 0644);
> +
>  static void queue_process(struct work_struct *work)
>  {
>  	struct netpoll_info *npinfo =
> @@ -732,7 +736,7 @@ int netpoll_setup(struct netpoll *np)
>  		}
>  
>  		atleast = jiffies + HZ/10;
> -		atmost = jiffies + 4*HZ;
> +		atmost = jiffies + carrier_timeout * HZ;
>  		while (!netif_carrier_ok(ndev)) {
>  			if (time_after(jiffies, atmost)) {
>  				printk(KERN_NOTICE
> -- 
> 1.6.3.3
> 
I don't mind this functionality at all, but I'm looking at the code, and I have
a hard time understanding why we bring up an interface here at all.  I get that
we might want early netpoll access for netconsole or something like that, but
looking at the console code I don't see where we buffer anything other than the
standard dmesg log.  I don't see much reason why we can't just let normal early
interface initalization from an initramfs bring up an interface like it normally
does.

Neil

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