On Sun, Dec 05, 2004 at 04:30:47PM +0100, Martin Josefsson wrote:

quoted

I verified that I get the same results on a small whimpy 82540EM
that runs at 32/66 as well. Just about to see what I get at 32/33
with that card.

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

60      350229
64      247037
68      219643
72      218205
76      216786
80      215386
84      214003
88      212638
92      211291
96      210004
100     208647
104     182461
108     181468
112     180453
116     179482
120     185472
124     188336
128     153743

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

60      431967
61      431311
62      431927
63      427827
64      427482

And with Scott's notxints patch:

60      514496
61      514493
62      514754
63      504629
64      504123

Sorry, forgot to answer your other questions, I'm a bit excited at the
moment :)

Makes sense :)

The 64/66 bus on this motherboard is directly connected to the
northbridge.

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

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 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.


--L