[ECOS] High priority thread versus network - FOLLOW-UP

Wayne Visser wvisser@lszpaper.com
Tue Aug 14 13:18:00 GMT 2007


Wayne Visser wrote:
> Hello all,
> 
> We're having a problem with an eCos app that has a relatively 
> long-running, high priority thread (runs at priority 2 every 10 ms and 
> takes about 4ms to complete).  Under high network loads, the app will 
> crash with no asserts or panics.  If the high priority thread is 
> disabled, the app will run fine for days without problem under high net 
> loads.  Conversely, without any networking activity, the app runs fine 
> for days.
> <snip>


Hello all,

This is a follow-up to some mysterious crashes we were seeing related to 
network activity.  Related posts are here:

https://bugzilla.ecoscentric.com/show_bug.cgi?id=1000403
http://sourceware.org/ml/ecos-discuss/2007-03/msg00024.html
http://sourceware.org/ml/ecos-discuss/2007-05/msg00046.html

This was seen on an i386 platform (Advantech PCM3370) and we noticed 
that when the AGP aperture was reduced the observed problem apparently 
'disappeared' leaving me to think we had some type of memory conflict 
between the aperture and the ethernet card.

Whether or not a high-priority thread was running and stealing time away 
from the networking threads turned out not be causal - network activity 
on its own was enough to cause crashes.  No asserts or panics were 
raised at a crash (apart from me perhaps :-0

It's not entirely clear why a change (specifically a reduction) in AGP 
aperture eliminates the assumed memory conflict.  We also observed that 
crashing was most frequent when the aperture was set to 1/2 of the main 
memory size.

The board uses a Via VT8606 Northbridge (ProSavage PN133T) and on our 
board's BIOS, it's possible to reduce but not completely disable the 
aperture so we did some research and have a method to disable it 
programmatically, which is probably better anyway.

Since this Northbridge is fairly common in PC104 boards, maybe someone 
else is seeing crashes in a similar way so here's how we ended up 
disabling the aperture.  NOTE:  This is not a totally satisfying fix, 
since we don't completely understand the problem, but in the 2 months 
that we've started doing this we have not recorded a single crash on our 
test boards.


// *******************************************************************
#include <cyg/io/pci.h>

// <snip>
// ...
// ...
// ...

// *******************************************************************
#define DEBUG_VT8606_SETUP      0

// <snip>
// ...
// ...
// ...


// *******************************************************************
// device/vendor id matching function for VT8606 Northbridge
//
static cyg_bool
pci_find_match_func(cyg_uint16 v, cyg_uint16 d, cyg_uint32 c, void *p)
{
   // vendor ID for Via Technologies = 0x1106
   // device ID for VT8606 = 0x0605
   return ((v == 0x1106) && (d == 0x0605));
}


// *******************************************************************
// Disable graphics aperture feature in Via VT8606 Northbridge.  Call
// this function as soon after startup as possible (i.e. before setting
// up PCI devices).  This function is benign if no VT8606 exists.
//
static void
chipset_init(void)
{
   cyg_pci_device_id pci_device_id;
   cyg_pci_device    pci_device_info;
#if DEBUG_VT8606_SETUP > 0
   cyg_uint8         b;
#endif
   cyg_uint32        dw;

   pci_device_id = CYG_PCI_NULL_DEVID;
   cyg_pci_init();
   if ( cyg_pci_find_matching(&pci_find_match_func, NULL,
                                &pci_device_id))
   {
     cyg_pci_get_device_info(pci_device_id, &pci_device_info);

     if (cyg_pci_configure_device(&pci_device_info))
     {

       // read GA base
#if DEBUG_VT8606_SETUP > 0
       cyg_pci_read_config_uint32(pci_device_info.devid, 0x10, &dw);
       diag_printf(" GA BASE (0x88):    0x%08x\n", dw);
#endif

       // read TLB and disable aperture
       cyg_pci_read_config_uint32(pci_device_info.devid, 0x88, &dw);
#if DEBUG_VT8606_SETUP > 0
       diag_printf(" GA TLB (0x88):    0x%08x\n", dw);
#endif
       dw &= ~2;
       cyg_pci_write_config_uint32(pci_device_info.devid, 0x88, dw);
#if DEBUG_VT8606_SETUP > 0
       cyg_pci_read_config_uint32(pci_device_info.devid, 0x88, &dw);
       diag_printf(" GA TLB (after disabling aperture) (0x88): 
0x%08x\n", dw);
#endif

       // read aperture size and set to 0
#if DEBUG_VT8606_SETUP > 0
       cyg_pci_read_config_uint8(pci_device_info.devid, 0x84, &b);
       diag_printf(" Aperture Size (0x84):    0x%02x\n", b);
#endif
       cyg_pci_write_config_uint8(pci_device_info.devid, 0x84, 0);
#if DEBUG_VT8606_SETUP > 0
       cyg_pci_read_config_uint8(pci_device_info.devid, 0x84, &b);
       diag_printf(" Aperture Size (after setting to 0) (0x84): 
0x%02x\n", b);
#endif
     }
   }
}

// *******************************************************************

--
Wayne Visser
LSZ PaperTech Inc.




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