netdev - Re: [net-next PATCH 1/2] igbvf: add new driver to support 82576 virtual functions

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Message-ID: <49C1948F.1060300@intel.com>
Date:	Wed, 18 Mar 2009 17:40:47 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"greg@...ah.com" <greg@...ah.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Zhao, Yu" <yu.zhao@...el.com>
Subject: Re: [net-next PATCH 1/2] igbvf: add new driver to support 82576 virtual
 functions

Andrew Morton wrote:
> On Wed, 18 Mar 2009 08:22:46 -0700 Alexander Duyck <alexander.h.duyck@...el.com> wrote:
> 
>>>>>> +static int igbvf_set_ringparam(struct net_device *netdev,
>>>>>> +                               struct ethtool_ringparam *ring)
>>>>>> +{
>>>>>> +     struct igbvf_adapter *adapter = netdev_priv(netdev);
>>>>>> +     struct igbvf_ring *tx_ring, *tx_old;
>>>>>> +     struct igbvf_ring *rx_ring, *rx_old;
>>>>>> +     int err;
>>>>>> +
>>>>>> +     if ((ring->rx_mini_pending) || (ring->rx_jumbo_pending))
>>>>>> +             return -EINVAL;
>>>>>> +
>>>>>> +     while (test_and_set_bit(__IGBVF_RESETTING, &adapter->state))
>>>>>> +             msleep(1);
>>>>> No timeout needed here?  Interrupts might not be working, for example..
>>>> This bit isn't set in interrupt context.  This is always used out of 
>>>> interrupt context and is just to prevent multiple setting changes at the 
>>>> same time.
>>> Oh.  Can't use plain old mutex_lock()?
>> We have one or two spots that actually check to see if the bit is set 
>> and just report a warning instead of actually waiting on the bit to clear.
> 
> mutex_is_locked()?

I suppose that would work, but I still would prefer to keep this bit of 
code as it is.  My main motivation is just to use what was already 
proven, and the fact is the e1000, e1000e, igb, and several other 
drivers all use this same approach and it works.

I don't think we need the extra overhead of the mutex lock since most of 
the calls that end up setting the __IGBVF_RESETTING bit will already be 
wrapped within rtnl_lock/unlock calls.  As far as I can tell it looks 
like the only two threads that would ever be competing for the lock 
would be the igbvf_reinit_locked and whatever ethtool or ifconfig 
requests that decide to make changes to the configuration of the netdevice.

Thanks,

Alex
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