printk delay for every callback does not make sense, change to delay every line
Signed-off-by: Dave Young <[email protected]>
---
kernel/printk.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-2.6.orig/kernel/printk.c 2010-02-02 13:38:47.646659531 +0800
+++ linux-2.6/kernel/printk.c 2010-02-02 13:39:19.446657319 +0800
@@ -678,7 +678,6 @@ asmlinkage int vprintk(const char *fmt,
char *p;
boot_delay_msec();
- printk_delay();
preempt_disable();
/* This stops the holder of console_sem just where we want him */
@@ -746,6 +745,7 @@ asmlinkage int vprintk(const char *fmt,
*/
for ( ; *p; p++) {
if (new_text_line) {
+ printk_delay();
/* Always output the token */
emit_log_char('<');
emit_log_char(current_log_level + '0');
On Sat, 6 Feb 2010 21:34:25 +0800
Dave Young <[email protected]> wrote:
> printk delay for every callback does not make sense, change to delay every line
>
> Signed-off-by: Dave Young <[email protected]>
> ---
>
> kernel/printk.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- linux-2.6.orig/kernel/printk.c 2010-02-02 13:38:47.646659531 +0800
> +++ linux-2.6/kernel/printk.c 2010-02-02 13:39:19.446657319 +0800
> @@ -678,7 +678,6 @@ asmlinkage int vprintk(const char *fmt,
> char *p;
>
> boot_delay_msec();
> - printk_delay();
>
> preempt_disable();
> /* This stops the holder of console_sem just where we want him */
> @@ -746,6 +745,7 @@ asmlinkage int vprintk(const char *fmt,
> */
> for ( ; *p; p++) {
> if (new_text_line) {
> + printk_delay();
> /* Always output the token */
> emit_log_char('<');
> emit_log_char(current_log_level + '0');
This moves the printk_delay() so that it is now inside
spin_lock_irqsave(logbuf_lock).
This fixes the race I mentioned in the previous email, but it seems a
bad idea. If the delay is long enough, it could even cause other CPUs
to get hit by the NMI watchdog when trying to acquire logbuf_lock.
A better approach would be to perform the calculation of "how long must
I delay" at this site, but perform the actual delay later, after the
raw_local_irq_restore(). This means that if the printk contains
"a\nb\nc\n" then we won't delay until the final \n, but that seems a
fairly small problem.
On Tue, Feb 9, 2010 at 6:06 AM, Andrew Morton <[email protected]> wrote:
> On Sat, 6 Feb 2010 21:34:25 +0800
> Dave Young <[email protected]> wrote:
>
>> printk delay for every callback does not make sense, change to delay every line
>>
>> Signed-off-by: Dave Young <[email protected]>
>> ---
>>
>> kernel/printk.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- linux-2.6.orig/kernel/printk.c 2010-02-02 13:38:47.646659531 +0800
>> +++ linux-2.6/kernel/printk.c 2010-02-02 13:39:19.446657319 +0800
>> @@ -678,7 +678,6 @@ asmlinkage int vprintk(const char *fmt,
>> char *p;
>>
>> boot_delay_msec();
>> - printk_delay();
>>
>> preempt_disable();
>> /* This stops the holder of console_sem just where we want him */
>> @@ -746,6 +745,7 @@ asmlinkage int vprintk(const char *fmt,
>> */
>> for ( ; *p; p++) {
>> if (new_text_line) {
>> + printk_delay();
>> /* Always output the token */
>> emit_log_char('<');
>> emit_log_char(current_log_level + '0');
>
> This moves the printk_delay() so that it is now inside
> spin_lock_irqsave(logbuf_lock).
>
> This fixes the race I mentioned in the previous email, but it seems a
> bad idea. If the delay is long enough, it could even cause other CPUs
> to get hit by the NMI watchdog when trying to acquire logbuf_lock.
>
> A better approach would be to perform the calculation of "how long must
> I delay" at this site, but perform the actual delay later, after the
> raw_local_irq_restore(). This means that if the printk contains
> "a\nb\nc\n" then we won't delay until the final \n, but that seems a
> fairly small problem.
>
Ok, agree. But need another variable to track '\n', if there's no line
break then
it will not delay at the end of printk.
--
Regards
dave