netdev - Re: [Xen-devel] [PATCHv1] xen-netfront: always keep the Rx ring full of requests

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Message-Id: <20141006.170748.1817067290457286845.davem@redhat.com>
Date:	Mon, 06 Oct 2014 17:07:48 -0400 (EDT)
From:	David Miller <davem@...hat.com>
To:	annie.li@...cle.com
Cc:	david.vrabel@...rix.com, netdev@...r.kernel.org,
	boris.ostrovsky@...cle.com, xen-devel@...ts.xenproject.org
Subject: Re: [Xen-devel] [PATCHv1] xen-netfront: always keep the Rx ring
 full of requests

From: annie li <annie.li@...cle.com>
Date: Mon, 06 Oct 2014 14:41:48 -0400

> 
> On 2014/10/6 12:00, David Vrabel wrote:
>>>>    +    queue->rx.req_prod_pvt = req_prod;
>>>> +
>>>> +    /* Not enough requests? Try again later. */
>>>> +    if (req_prod - queue->rx.rsp_cons < NET_RX_SLOTS_MIN) {
>>>> +        mod_timer(&queue->rx_refill_timer, jiffies + (HZ/10));
>>>> +        return;
>>> If the previous for loop breaks because of failure of
>>> xennet_alloc_one_rx_buffer, then notify_remote_via_irq is missed here
>>> if
>>> the code returns directly.
>> This is deliberate -- there's no point notifying the backend if there
>> aren't enough requests for the next packet.  Since we don't know what
>> the next packet might be we assume it's the largest possible.
> That makes sense.
> However, the largest packet case does not happen so
> frequently. Moreover, netback checks the slots every incoming skb
> requires in xenvif_rx_ring_slots_available, not only concerning the
> largest case.

I have an opinion about the sysfs stuff.

It's user facing, so even if it doesn't influence behavior any more
you have to keep the files around, just make them nops.
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