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  1. 23 Aug, 2004 5 commits
    • Akiyama Nobuyuki's avatar
      [PATCH] NMI trigger switch support for debugging(updated) · 7f2b65bd
      Akiyama Nobuyuki authored 
      I made a patch for debugging with the help of NMI trigger switch.
When kernel hangs severely, keyboard operation(e.g.Ctrl-Alt-Del)
doesn't work properly. This patch enables debugging information
to be displayed on console in this case.
I think this feature is necessary as standard functionality.
Please feel free to use this patch and let me know if you have
any comments.

Background:

When a trouble occurs in kernel, we usually begin to investigate
with following information:
 - panic >> panic message.
 - oops >> CPU registers and stack trace.
 - hang >> **NONE** no standard method established.

How it works:

Most IA32 servers have a NMI switch that fires NMI interrupt up.
The NMI interrupt can interrupt even if kernel is serious state,
for example deadlock under the interrupt disabled.
When the NMI switch is pressed after this feature is activated,
CPU registers and stack trace are displayed on console and then
panic occurs.
This feature is activated or deactivated with sysctl.

On IA32 architecture, only the following are defined as reason
of NMI interrupt:
 - memory parity error
 - I/O check error
The reason code of NMI switch is not defined, so this patch assumes
that all undefined NMI interrupts are fired by MNI switch.
However, oprofile and NMI watchdog also use undefined NMI interrupt.
Therefore this feature cannot be used at the same time with oprofile
and NMI watchdog. This feature hands NMI interrupt over to oprofile
and NMI watchdog. So, when they have been activated, this feature
doesn't work even if it is activated.

Supported architecture:

IA32

Setup:

Set up the system control parameter as follows:

# sysctl -w kernel.unknown_nmi_panic=1
kernel.unknown_nmi_panic = 1

If the NMI switch is pressed, CPU registers and stack trace will
be displayed on console and then panic occurs.
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      7f2b65bd
    • Arnd Bergmann's avatar
      [PATCH] fix reading string module parameters in sysfs · f1577452
      Arnd Bergmann authored 
      Reading the contents of a module_param_string through sysfs currently
oopses because the param_get_charp() function cannot operate on a
kparam_string struct.  This introduces the required param_get_string.
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      f1577452
    • Mike Kravetz's avatar
      [PATCH] proc fs task name locking fix · 4b4b699d
      Mike Kravetz authored 
      Races have been observed between excec-time overwriting of task->comm and
/proc accesses to the same data.  This causes environment string
information to appear in /proc.

Fix that up by taking task_lock() around updates to and accesses to
task->comm.
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      4b4b699d
    • Randy Dunlap's avatar
      [PATCH] tg3 section fix · 9026a8d6
      Randy Dunlap authored 
      add_pin_to_irq() should not be __init; it is used after init code.
Signed-off-by: default avatarRandy Dunlap <rddunlap@osdl.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      9026a8d6
    • Ingo Molnar's avatar
      [PATCH] context-switching overhead in X, ioport() · a55702bb
      Ingo Molnar authored 
      while debugging/improving scheduling latencies i got the following
strange latency report from Lee Revell:

  http://krustophenia.net/testresults.php?dataset=2.6.8.1-P6#/var/www/2.6.8.1-P6

this trace shows a 120 usec latency caused by XFree86, on a 600 MHz x86
system. Looking closer reveals:

  00000002 0.006ms (+0.003ms): __switch_to (schedule)
  00000002 0.088ms (+0.082ms): finish_task_switch (schedule)

it took more than 80 usecs for XFree86 to do a context-switch!

it turns out that the reason for this (massive) context-switching
overhead is the following change in 2.6.8:

      [PATCH] larger IO bitmaps

To demonstrate the effect of this change i've written ioperm-latency.c
(attached), which gives the following on vanilla 2.6.8.1:

  # ./ioperm-latency
  default no ioperm:             scheduling latency: 2528 cycles
  turning on port 80 ioperm:     scheduling latency: 10563 cycles
  turning on port 65535 ioperm:  scheduling latency: 10517 cycles

the ChangeSet says:

        Now, with the lazy bitmap allocation and per-CPU TSS, this
        will really not drain any resources I think.

this is plain wrong. An increase in the IO bitmap size introduces
per-context-switch overhead as well: we now have to copy an 8K bitmap
every time XFree86 context-switches - even though XFree86 never uses
ports higher than 1024! I've straced XFree86 on a number of x86 systems
and in every instance ioperm() was used - so i'd say the majority of x86
Linux systems running 2.6.8.1 are affected by this problem.

This not only causes lots of overhead, it also trashes ~16K out of the
L1 and L2 caches, on every context-switch. It's as if XFree86 did a L1
cache flush on every context-switch ...

the simple solution would be to revert IO_BITMAP_BITS back to 1024 and
release 2.6.8.2?

I've implemented another solution as well, which tracks the
highest-enabled port # for every task and does the copying of the bitmap
intelligently. (patch attached) The patched kernel gives:

  # ./ioperm-latency
  default no ioperm:             scheduling latency: 2423 cycles
  turning on port 80 ioperm:     scheduling latency: 2503 cycles
  turning on port 65535 ioperm:  scheduling latency: 10607 cycles

this is much more acceptable - the full overhead only occurs in the very
unlikely event of a task using the high ioport range. X doesnt suffer
any significant overhead.

(tracking the maximum allowed port # also allows a simplification of
io_bitmap handling: e.g. we dont do the invalid-offset trick anymore -
the IO bitmap in the TSS is always valid and secure.)

I tested the patch on x86 SMP and UP, it works fine for me. I tested
boundary conditions as well, it all seems secure.

	Ingo

#include <errno.h>
#include <stdio.h>
#include <sched.h>
#include <signal.h>
#include <sys/io.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/unistd.h>

#define CYCLES(x) asm volatile ("rdtsc" :"=a" (x)::"edx")

#define __NR_sched_set_affinity 241
_syscall3 (int, sched_set_affinity, pid_t, pid, unsigned int, mask_len, unsigned long *, mask)

/*
 * Use a pair of RT processes bound to the same CPU to measure
 * context-switch overhead:
 */
static void measure(void)
{
	unsigned long i, min = ~0UL, pid, mask = 1, t1, t2;

	sched_set_affinity(0, sizeof(mask), &mask);

	pid = fork();
	if (!pid)
		for (;;) {
			asm volatile ("sti; nop; cli");
			sched_yield();
		}

	sched_yield();
	for (i = 0; i < 100; i++) {
		asm volatile ("sti; nop; cli");
		CYCLES(t1);
		sched_yield();
		CYCLES(t2);
		if (i > 10) {
			if (t2 - t1 < min)
				min = t2 - t1;
		}
	}
	asm volatile ("sti");

	kill(pid, 9);
	printf("scheduling latency: %ld cycles\n", min);
	sched_yield();
}

int main(void)
{
	struct sched_param p = { sched_priority: 2 };
	unsigned long mask = 1;

	if (iopl(3)) {
		printf("need to run as root!\n");
		exit(-1);
	}
	sched_setscheduler(0, SCHED_FIFO, &p);
	sched_set_affinity(0, sizeof(mask), &mask);

	printf("default no ioperm:             ");
	measure();

	printf("turning on port 80 ioperm:     ");
	ioperm(0x80,1,1);
	measure();

	printf("turning on port 65535 ioperm:  ");
	if (ioperm(0xffff,1,1))
		printf("FAILED - older kernel.\n");
	else
		measure();

	return 0;
}
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      a55702bb
  3. 22 Aug, 2004 20 commits
  5. 20 Aug, 2004 8 commits
  7. 19 Aug, 2004 7 commits
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