I have a via motherboard with C3 processor and some real-tek NICs.  I 
noticed
when using the top-of-tree that performance on it sucked (30Mbps v/s 54Mbps
network throughput in one pertinent test).

After several hours of bisecting, I see this as the culprit:

7b37b5fd9ba32c0c5afc3537eed7e7466f2173e2 is first bad commit
commit 7b37b5fd9ba32c0c5afc3537eed7e7466f2173e2
Author: Len Brown <len.brown@intel.com>
Date:   Tue Dec 23 01:47:42 2008 -0500

    ACPI: disable MPS when NO APIC-table found
   
    When ACPI is asked to find an MADT (APIC table)
    and fails, then ACPI expects to run in PIC mode.
   
    However, if an MP Table is was found, IRQs will be
    registered as if an IOAPIC is being used, even
    though ACPI is configuring interrupt links links for PIC mode.
   
    In this scenario, disable MPS so that IRQs
    are registered in PIC mode, consistent with ACPI.
   
    http://bugzilla.kernel.org/show_bug.cgi?id=12257
   
    Signed-off-by: Len Brown <len.brown@intel.com>

:040000 040000 86ce74daee3a9fe6ff21ef7f8fb364af23ec0c1e 
364933dfec0df34e63b1aeff6aff4092d421886b M      arch


In addition, I see this warning in my logs, which is likely the symptom:

ACPI Exception (tbxface-0627): AE_NO_ACPI_TABLES, While loading 
namespace from ACPI tables ]
ACPI: Unable to load the System Description Tables
------------[ cut here ]------------
WARNING: at 
/home/greearb/git/linux-2.6.linus/kernel/time/clockevents.c:46 
clockevent_delta)
Modules linked in:
Pid: 1, comm: swapper Not tainted 2.6.28-rc9c3 #17
Call Trace:
 [<c0124d9f>] warn_on_slowpath+0x5f/0x90
 [<c04d5b9d>] lapic_cal_handler+0x8d/0xe0
 [<c0378d00>] _spin_lock_irqsave+0x20/0x30
 [<c0378ea4>] _spin_unlock_irqrestore+0x14/0x30
 [<c0155cbb>] handle_level_irq+0x9b/0xe0
 [<c012977d>] irq_exit+0x4d/0x80
 [<c0105eb5>] do_IRQ+0x55/0xb0
 [<c01409d0>] tick_handle_periodic+0x0/0x70
 [<c0104643>] common_interrupt+0x23/0x30
 [<c01409d0>] tick_handle_periodic+0x0/0x70
 [<c014042f>] clockevent_delta2ns+0xaf/0xc0
 [<c04d5779>] setup_boot_APIC_clock+0x1e9/0x580
 [<c01208ef>] schedule_tail+0xf/0x40
 [<c0115665>] setup_apic_nmi_watchdog+0x15/0x60
 [<c04d5d1d>] APIC_init_uniprocessor+0x8d/0x100
 [<c04c67c7>] kernel_init+0x47/0xe0
 [<c04c6780>] kernel_init+0x0/0xe0
 [<c01047f7>] kernel_thread_helper+0x7/0x10
---[ end trace 4eaa2a86a8e2da22 ]---
APIC frequency too slow, disabling apic timer


The full dmesg of this boot and kernel .config is attached.

Please let me know if I can offer additional info to help get this 
properly fixed.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com> 
Candela Technologies Inc  http://www.candelatech.com