netdev - Re: [net-next 11/13] igb: Make Tx budget for NAPI user adjustable

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Message-ID: <4E776441.9090602@intel.com>
Date:	Mon, 19 Sep 2011 08:48:17 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net,
	netdev@...r.kernel.org, gospo@...hat.com
Subject: Re: [net-next 11/13] igb: Make Tx budget for NAPI user adjustable

On 09/17/2011 10:04 AM, Ben Hutchings wrote:
> On Sat, 2011-09-17 at 01:04 -0700, Jeff Kirsher wrote:
>> From: Alexander Duyck<alexander.h.duyck@...el.com>
>>
>> This change is meant to make the NAPI budget limits for transmit
>> adjustable.  By doing this it is possible to tune the value for optimal
>> performance with applications such as routing.
> [...]
>> --- a/drivers/net/ethernet/intel/igb/igb_ethtool.c
>> +++ b/drivers/net/ethernet/intel/igb/igb_ethtool.c
>> @@ -1989,6 +1989,9 @@ static int igb_set_coalesce(struct net_device *netdev,
>>   	if ((adapter->flags&  IGB_FLAG_QUEUE_PAIRS)&&  ec->tx_coalesce_usecs)
>>   		return -EINVAL;
>>
>> +	if (ec->tx_max_coalesced_frames_irq)
>> +		adapter->tx_work_limit = ec->tx_max_coalesced_frames_irq;
>> +
> [...]
>
> I don't think it really makes sense to conflate NAPI and interrupt
> moderation parameters.  This really ought to be added to NAPI itself.
>
> (NAPI contexts really ought to be exposed through sysfs somehow.  I
> think we've discussed this before, and it's tricky due to the lack of a
> consistent mapping between those contexts and net devices.)
>
> Ben.

All NAPI does is move things from a hard interrupt to a soft interrupt 
in the case of TX cleanup.  If it wasn't for NAPI we would be calling 
ixgbe_clean_tx_irq directly from the interrupt handler and would still 
be using the same limiting value.  This is why placing it here makes sense.

Thanks,

Alex
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