netdev - Re: [PATCH net-next] ibmvnic: Defer tx completion processing using a wait queue

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Message-ID: <570D61E7.2090203@linux.vnet.ibm.com>
Date:	Tue, 12 Apr 2016 16:00:23 -0500
From:	John Allen <jallen@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>,
	netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH net-next] ibmvnic: Defer tx completion processing using a
 wait queue

On 04/12/2016 03:12 PM, Eric Dumazet wrote:
> On Tue, 2016-04-12 at 14:38 -0500, John Allen wrote:
>> Moves tx completion processing out of interrupt context, deferring work
>> using a wait queue. With this work now deferred, we must account for the
>> possibility that skbs can be sent faster than we can process completion
>> requests in which case the tx buffer will overflow. If the tx buffer is
>> full, ibmvnic_xmit will return NETDEV_TX_BUSY and stop the current tx
>> queue. Subsequently, the queue will be restarted in ibmvnic_complete_tx
>> when all pending tx completion requests have been cleared.
> 
> 1) Why is this needed ?

In the current ibmvnic implementation, tx completion processing is done in
interrupt context. Depending on the load, this can block further
interrupts for a long time. This patch just creates a bottom half so that
when a tx completion interrupt comes in, we can defer the majority of the
work and exit interrupt context quickly.

> 
> 2) If it is needed, why is this not done in a generic way, so that other
> drivers can use this ?

I'm still fairly new to network driver development so I'm not in tune with
the needs of other drivers. My assumption was that the wait queue data
structure was a reasonably generic way to handle something like this. Is
there a more appropriate/generic way of implementing a bottom half for
this purpose?

-John
> 
> Thanks.
> 
> 
> 
>