Date: Tue, 23 Nov 2004 03:02:35 +0100 (CET) From: Sten Spans <sten@blinkenlights.nl> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-alpha@FreeBSD.org Subject: Re: alpha and em mtu Message-ID: <Pine.SOC.4.61.0411230259030.10997@tea.blinkenlights.nl> In-Reply-To: <Pine.SOC.4.61.0411230026430.10997@tea.blinkenlights.nl> References: <Pine.SOC.4.61.0411142153430.26307@tea.blinkenlights.nl> <Pine.SOC.4.61.0411222147180.10997@tea.blinkenlights.nl> <Pine.SOC.4.61.0411230026430.10997@tea.blinkenlights.nl>
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On Tue, 23 Nov 2004, Sten Spans wrote:
> On Mon, 22 Nov 2004, John Baldwin wrote:
>
>> On Monday 22 November 2004 04:15 pm, Sten Spans wrote:
>>>
>>> db> trace
>>> tcp_input() at tcp_input+0x3a4
>>> ip_input() at ip_input+0x9fc
>>> netisr_processqueue() at netisr_processqueue+0xac
>>> swi_net() at swi_net+0xf0
>>> ithread_loop() at ithread_loop+0x1d4
>>> fork_exit() at fork_exit+0x100
>>> exception_return() at exception_return
>>> --- root of call graph ---
>>>
>>> (gdb) l *tcp_input+0x3a4
>>> 0xfffffc00004cd054 is in tcp_input (/usr/src/sys/netinet/tcp_input.c:554).
>>> 549
>>> 550 /*
>>> 551 * Check that TCP offset makes sense,
>>> 552 * pull out TCP options and adjust length.
>>> XXX
>>> 553 */
>>> 554 off = th->th_off << 2;
>>> 555 if (off < sizeof (struct tcphdr) || off > tlen) {
>>> 556 tcpstat.tcps_rcvbadoff++;
>>> 557 goto drop;
>>> 558 }
>>> (gdb) l *ip_input+0x9fc
>>> 0xfffffc00004c355c is in ip_input (/usr/src/sys/netinet/ip_input.c:739).
>>> 734 /*
>>> 735 * Switch out to protocol's input routine.
>>> 736 */
>>> 737 ipstat.ips_delivered++;
>>> 738
>>> 739 (*inetsw[ip_protox[ip->ip_p]].pr_input)(m, hlen);
>>> 740 return;
>>> 741 bad:
>>> 742 m_freem(m);
>>> 743 }
>>> (gdb) l *netisr_processqueue+0xac
>>> 0xfffffc00004ad45c is in netisr_processqueue
>>> (/usr/src/sys/net/netisr.c:233).
>>> 228
>>> 229 for (;;) {
>>> 230 IF_DEQUEUE(ni->ni_queue, m);
>>> 231 if (m == NULL)
>>> 232 break;
>>> 233 ni->ni_handler(m);
>>> 234 }
>>> 235 }
>>
>> Hmm, so can you check here to see if the 'm' pointer in this routine is
>> misaligned? If so, then this may be a driver bug.
>>
>
> --- netisr.c.orig Tue Nov 23 00:21:38 2004
> +++ netisr.c Tue Nov 23 00:21:45 2004
> @@ -230,6 +230,8 @@
> IF_DEQUEUE(ni->ni_queue, m);
> if (m == NULL)
> break;
> + if (((uintptr_t)m & 0x3) != 0)
> + printf("%s: mbuf %p is misaligned\n", __func__, m);
> ni->ni_handler(m);
> }
> }
>
> doesn't seem to print anything, but ...
>
> if_em.c
> 2442
> 2443 /*if (ifp->if_mtu <= ETHERMTU) { */
> 2444 m_adj(mp, ETHER_ALIGN);
> 2445 /*} */
> 2446
>
> does seem to fix the crash, also trashes the performance,
> but that's another matter. It looks like mbuf alignment is
> needed, if_bge seems to provide reasonable examples.
And looking at netbsd/openbsd clarifies the whole issue,
#ifdef __STRICT_ALIGNMENT
/*
* The ethernet payload is not 32-bit aligned when
* Jumbo packets are enabled, so on architectures with
* strict alignment we need to shift the entire packet
* ETHER_ALIGN bytes. Ugh.
*/
This diff probably should be merged.
http://www.openbsd.org/cgi-bin/cvsweb/src/sys/dev/pci/if_em.c.diff?r1=1.22&r2=1.23
Although I don't know wether freebsd has the STRICT_ALIGNMENT define.
--
Sten Spans
"There is a crack in everything, that's how the light gets in."
Leonard Cohen - Anthem
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