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[Xen-users] vanilla linux, jumbo frames

On Tue, 18 Mar 2008, Tom Brown wrote:


 Isn't these 100 mbps or 1000 mbps speeds funny numbers for today's CPU
 power? I mean, somewhere in the design, there's something wrong that
 forces
 us to make possibly too many context switches between DomU, Hypervisor and
 Dom0. ???

 Emre

what, something like the 1500 byte maximum transmission unit (MTU) from back in the days when 10 MILLION bits per second was so insanely fast we connected everything to the same cable!? (remember 1200 baud modems?) Yes, there might be some "design" decisions that don't work all that well today.

AFAIK, XEN can't do oversize (jumbo) frames, that would be a big help for a lot of things (iSCSI, ATAoE, local network )... but even so, AFAIK it would only be a relatively small improvement (jumbo frames only going up to about 8k AFAIK).

-Tom

My bad, As Pasi pointed out, it turns out that XEN has supported jumbo frames since at least 3.0.4 ... of course, the AOE initiator support that actually uses it seems to not be available until kernels 2.6.19 ... which is too current for centos 5.1

so now I'm trying to boot 2.6.24.3 as a 32 PV guest on a 64 bit hypervisor, and it's dieing at

Checking if this processor honours the WP bit even in supervisor mode... Ok.
installing Xen timer for CPU 0
------------[ cut here ]------------
kernel BUG at arch/x86/xen/time.c:122!
invalid opcode: 0000 [#1] SMP

time.c 122 is the BUG line in the snippet below...

static void setup_runstate_info(int cpu)
{
        struct vcpu_register_runstate_memory_area area;

        area.addr.v = &per_cpu(runstate, cpu);

        if (HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area,
                               cpu, &area))
                BUG();
}



Is this 32 bit on 64 bit hypervisor supposed to work for vanilla linux?

-Tom

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