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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 7 Oct 2014 10:43:36 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	David Miller <davem@...hat.com>, <annie.li@...cle.com>
CC:	<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

On 06/10/14 22:07, David Miller wrote:
> 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.

An upcoming change to netback will cause it to wait for enough slots for
the largest possible packet.

> 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.

That's a good point.

David
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html