On Sun, 5 Dec 2004, Martin Josefsson wrote:

quoted

-#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.

It gives pretty varied results.
This is during a pktgen run.

The machine is an Athlon MP 2000+ which operated at 1667 MHz

e1000: MMIO read took 481 clocks
e1000: MMIO read took 369 clocks
e1000: MMIO read took 481 clocks
e1000: MMIO read took 11 clocks
e1000: MMIO read took 477 clocks
e1000: MMIO read took 316 clocks
e1000: MMIO read took 481 clocks
e1000: MMIO read took 316 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 332 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 372 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 11 clocks
e1000: MMIO read took 481 clocks
e1000: MMIO read took 388 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 11 clocks
e1000: MMIO read took 485 clocks
e1000: MMIO read took 317 clocks
e1000: MMIO read took 481 clocks
e1000: MMIO read took 337 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 316 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 409 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 334 clocks
e1000: MMIO read took 481 clocks
e1000: MMIO read took 316 clocks
e1000: MMIO read took 480 clocks
e1000: MMIO read took 11 clocks
e1000: MMIO read took 505 clocks
e1000: MMIO read took 359 clocks
e1000: MMIO read took 484 clocks
e1000: MMIO read took 337 clocks
e1000: MMIO read took 464 clocks
e1000: MMIO read took 504 clocks

/Martin