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SubjectRe: mmotm 2009-04-10-02-21 uploaded - forkbombed by work_for_cpu
On Mon, 13 Apr 2009 19:18:53 +0200 Ingo Molnar <mingo@elte.hu> wrote:

>
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > So I do think Andrew's commit is broken and we should think about
> > it a bit more, but I also think that Valdis' problem comes from
> > acpi-cpufreq just being damn stupid. Doing a
> > smp_call_function_single() to read two MSR's is going to be a
> > _lot_ more efficient than doing that crazy work_on_cpu() for that.
> >
> > So the _real_ problem came through the commits like
> >
> > cpufreq: use work_on_cpu in acpi-cpufreq.c for drv_read and drv_write
> > cpumask: use work_on_cpu in acpi-cpufreq.c for read_measured_perf_ctrs
> >
> > that were meant to reduce stack usage with big cpu masks. And
> > sure, the _old_ way of doing it was also stupid (it rescheduled
> > the process to the other CPU by using cpus_allowed()).
> >
> > Mike, Ingo?
>
> I think Andrew has a stack of fixes queued up, one of which should
> solve this problem too - which Mike tested - as the commit from
> Andrew has caused another regression as well.
>
> There's no sha1 - the patch is in this thread on lkml:
>
> sysbench(oltp)+mysql 10% regression with 2.6.30-rc1
>
> | From: Andrew Morton <akpm@linux-foundation.org>
> |
> | 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,
>

Yup. It's presently in Len's hands. And Rusty's.

Vladis, perhaps you can verify?


From: Andrew Morton <akpm@linux-foundation.org>

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@linux-foundation.org>
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.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mike Galbraith <efault@gmx.de>
Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c | 25 ++++++++-----------
1 file changed, 11 insertions(+), 14 deletions(-)
diff -puN arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-using-work_on_cpu arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
--- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-using-work_on_cpu
+++ a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
@@ -153,7 +153,8 @@ struct drv_cmd {
u32 val;
};

-static long do_drv_read(void *_cmd)
+/* Called via smp_call_function_single(), on the target CPU */
+static void do_drv_read(void *_cmd)
{
struct drv_cmd *cmd = _cmd;
u32 h;
@@ -170,10 +171,10 @@ static long do_drv_read(void *_cmd)
default:
break;
}
- return 0;
}

-static long do_drv_write(void *_cmd)
+/* Called via smp_call_function_single(), on the target CPU */
+static void do_drv_write(void *_cmd)
{
struct drv_cmd *cmd = _cmd;
u32 lo, hi;
@@ -192,23 +193,21 @@ static long do_drv_write(void *_cmd)
default:
break;
}
- return 0;
}

static void drv_read(struct drv_cmd *cmd)
{
cmd->val = 0;

- work_on_cpu(cpumask_any(cmd->mask), do_drv_read, cmd);
+ smp_call_function_single(cpumask_any(cmd->mask), do_drv_read, cmd, 1);
}

static void drv_write(struct drv_cmd *cmd)
{
- unsigned int i;
+ unsigned int cpu;

- for_each_cpu(i, cmd->mask) {
- work_on_cpu(i, do_drv_write, cmd);
- }
+ 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)
@@ -252,15 +251,13 @@ struct perf_pair {
} aperf, mperf;
};

-
-static long read_measured_perf_ctrs(void *_cur)
+/* Called via smp_call_function_single(), on the target CPU */
+static void read_measured_perf_ctrs(void *_cur)
{
struct perf_pair *cur = _cur;

rdmsr(MSR_IA32_APERF, cur->aperf.split.lo, cur->aperf.split.hi);
rdmsr(MSR_IA32_MPERF, cur->mperf.split.lo, cur->mperf.split.hi);
-
- return 0;
}

/*
@@ -283,7 +280,7 @@ static unsigned int get_measured_perf(st
unsigned int perf_percent;
unsigned int retval;

- if (!work_on_cpu(cpu, read_measured_perf_ctrs, &readin))
+ if (smp_call_function_single(cpu, read_measured_perf_ctrs, &cur, 1))
return 0;

cur.aperf.whole = readin.aperf.whole -
_


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