On Sun, 5 Dec 2004, Lennert Buytenhek wrote:

quoted

Just tested the 82540EM at 32/33 and it's a big diffrence.

60      350229
64      247037
68      219643

[snip]

With or without prefetching? My 82540 in 32/33 mode gets on baseline
2.6.9:

With, will test without. I've always suspected that the 32bit bus on this
motherboard is a bit slow.

Your lspci output seems to suggest there is another PCI bridge in
between (00:10.0)

Yes it sits between the 32bit and the 64bit bus.

Basically on my box, it's CPU - MCH - P64H2 - e1000, where MCH is the
'Memory Controller Hub' and P64H2 the PCI-X bridge chip.

I don't have PCI-X (unless 64/66 counts as PCI-x which I highly doubt)

quoted

I have no idea how expensive an MMIO read is on this machine, do you have
an relatively easy way to find out?

A dirty way, yes ;-)  Open up e1000_osdep.h and do:

-#define E1000_READ_REG(a, reg) ( \
-    readl((a)->hw_addr + \
-        (((a)->mac_type >= e1000_82543) ? E1000_##reg : E1000_82542_##reg)))
+#define E1000_READ_REG(a, reg) ({ \
+    unsigned long s, e, d, v; \
+\
+    (a)->mmio_reads++; \
+    rdtsc(s, d); \
+    v = readl((a)->hw_addr + \
+        (((a)->mac_type >= e1000_82543) ? E1000_##reg : E1000_82542_##reg)); \
+    rdtsc(e, d); \
+    e -= s; \
+    printk(KERN_INFO "e1000: MMIO read took %ld clocks\n", e); \
+    printk(KERN_INFO "e1000: in process %d(%s)\n", current->pid, current->comm); \
+    dump_stack(); \
+    v; \
+})

You might want to disable the stack dump of course.

Will test this in a while.

/Martin