Re: mmotm 2009-04-10-02-21 uploaded - forkbombed by work_for_cpu

[Andrew Morton]

On Wed, 15 Apr 2009 12:45:34 +0430 Ali Gholami Rudi <ali@xxxxxxx> wrote:

> Hi,
> 
> In today's tip (v2.6.30-rc2), when my cpu is idle (and the ondemand
> governor correctly uses the lowest frequency) the temperature of my CPU
> rises to above 50^C till the fan turns on (it used to be about 40^C
> before).  Git bisect points to this patch:
> 
>   commit 01599fca6758d2cd133e78f87426fc851c9ea725
>   Author: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>   Date:   Mon Apr 13 10:27:49 2009 -0700
>   
>       cpufreq: use smp_call_function_[single|many]() in acpi-cpufreq.c
>       
>       Atttempting to rid us of the problematic work_on_cpu().  Just use
>       smp_call_fuction_single() here.
>       
>       This repairs a 10% sysbench(oltp)+mysql regression which Mike reported,
>       due to
>       
>         commit 6b44003e5ca66a3fffeb5bc90f40ada2c4340896
>         Author: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>         Date:   Thu Apr 9 09:50:37 2009 -0600
>       
>             work_on_cpu(): rewrite it to create a kernel thread on demand
>       
>       It seems that the kernel calls these acpi-cpufreq functions at a quite
>       high frequency.
>       
>       Valdis Kletnieks also reports that this causes 70-90 forks per second on
>       his hardware.
>       
>       Cc: Valdis.Kletnieks@xxxxxx
>       Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
>       Cc: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
>       Cc: Len Brown <len.brown@xxxxxxxxx>
>       Cc: Zhao Yakui <yakui.zhao@xxxxxxxxx>
>       Acked-by: Dave Jones <davej@xxxxxxxxxx>
>       Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>       Tested-by: Mike Galbraith <efault@xxxxxx>
>       Cc: "Zhang, Yanmin" <yanmin_zhang@xxxxxxxxxxxxxxx>
>       Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>       Acked-by: Ingo Molnar <mingo@xxxxxxx>
>       [ Made it use smp_call_function_many() instead of looping over cpu's
>         with smp_call_function_single()    - Linus ]

<stares suspiciously at smp_call_function_many()>

 * smp_call_function_many(): Run a function on a set of other CPUs.

"other".  It refuses to call the function on *this* CPU.  Tricky.

Does this fix it up?

--- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~a
+++ a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
@@ -204,7 +204,10 @@ static void drv_read(struct drv_cmd *cmd
 
 static void drv_write(struct drv_cmd *cmd)
 {
-	smp_call_function_many(cmd->mask, do_drv_write, cmd, 1);
+	unsigned cpu;
+
+	for_each_cpu(cpu, cmd->mask)
+		smp_call_function_single(cpu, do_drv_write, cmd, 1);	
 }
 
 static u32 get_cur_val(const struct cpumask *mask)
_

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