On Tue, 2008-09-16 at 14:43 +0530, Arun R Bharadwaj wrote:
> The implentation details of this as follows:
80 char lines please
> A sysfs entry is created
> at /sys/devices/system/cpu/cpuX/timer_migration. By setting this to 1,
> timer migration is enabled for that cpu.
> An important thing to note here is cpu-pinned timers. Timers can be
> pinned to a particular cpu using the function add_timer_on(). So, such
> timers should not be migrated.
You utterly fail to mention hrtimers even though you do touch those as
well, what's more - there are hrtimers that need to be run on the cpu
that queues them - you don't seem to provide anything like that.
> Since the last 3 bits of the tvec_base is guaranteed to be 0, and
> since the last bit is being used to indicate deferrable timers, I'm
> using the second last bit to indicate cpu-pinned timers.
> The implementation of functions to manage the TBASE_PINNED_FLAG is
> similar to those which manage the TBASE_DEFERRABLE_FLAG.
>
> Signed-off-by: Arun Bharadwaj <arun@xxxxxxxxxxxxxxxxxx>
> ---
please add --show-c-function to your diff
> Index: linux-2.6.26/drivers/base/cpu.c
> ===================================================================
> --- linux-2.6.26.orig/drivers/base/cpu.c 2008-09-15 08:14:40.000000000 +0000
> +++ linux-2.6.26/drivers/base/cpu.c 2008-09-15 09:34:52.000000000 +0000
> @@ -13,6 +13,7 @@
>
> #include "base.h"
>
> +DEFINE_PER_CPU(int, enable_timer_migration);
> struct sysdev_class cpu_sysdev_class = {
> .name = "cpu",
> };
> @@ -20,6 +21,21 @@
>
> static DEFINE_PER_CPU(struct sys_device *, cpu_sys_devices);
>
> +#ifdef CONFIG_TIMER_MIGRATION
> +static ssize_t timer_migration_show(struct sys_device *dev, char *buf)
> +{
> + struct cpu *cpu = container_of(dev, struct cpu, sysdev);
> + return sprintf(buf, "%u\n", per_cpu(enable_timer_migration, cpu->sysdev.id));
> +}
> +static ssize_t timer_migration_store(struct sys_device *dev, const char *buf, size_t count)
> +{
> + struct cpu *cpu = container_of(dev, struct cpu, sysdev);
> + per_cpu(enable_timer_migration, cpu->sysdev.id) = buf[0] - 48;
> + return count;
> +}
> +static SYSDEV_ATTR(timer_migration, 0666, timer_migration_show, timer_migration_store);
> +#endif
Why bother with the CONFIG_ variable - its so little code and it adds to
the Kconfig space.
> #ifdef CONFIG_HOTPLUG_CPU
> static ssize_t show_online(struct sys_device *dev, char *buf)
> {
> @@ -175,6 +191,11 @@
> if (!error)
> error = sysdev_create_file(&cpu->sysdev, &attr_crash_notes);
> #endif
> +
> +#ifdef CONFIG_TIMER_MIGRATION
> + if (!error)
> + error = sysdev_create_file(&cpu->sysdev, &attr_timer_migration);
> +#endif
> return error;
> }
>
> Index: linux-2.6.26/init/Kconfig
> ===================================================================
> --- linux-2.6.26.orig/init/Kconfig 2008-09-15 08:14:40.000000000 +0000
> +++ linux-2.6.26/init/Kconfig 2008-09-15 08:14:48.000000000 +0000
> @@ -923,3 +923,9 @@
> designed for best read-side performance on non-realtime
> systems. Classic RCU is the default. Note that the
> PREEMPT_RCU symbol is used to select/deselect this option.
> +
> +config TIMER_MIGRATION
> + bool
> + default y
> + help
> + This option enables migration of non cpu-affine timers to cpu0.
this will earn you a place in the hall of kconfig-help-text of shame.
> Index: linux-2.6.26/include/linux/timer.h
> ===================================================================
> --- linux-2.6.26.orig/include/linux/timer.h 2008-09-15 08:14:40.000000000 +0000
> +++ linux-2.6.26/include/linux/timer.h 2008-09-15 08:31:27.000000000 +0000
> @@ -5,6 +5,7 @@
> #include <linux/ktime.h>
> #include <linux/stddef.h>
> #include <linux/debugobjects.h>
> +#include <linux/percpu.h>
>
> struct tvec_base;
>
> @@ -187,3 +188,7 @@
> unsigned long round_jiffies_relative(unsigned long j);
>
> #endif
> +
> +#ifdef CONFIG_TIMER_MIGRATION
> +DECLARE_PER_CPU(int, enable_timer_migration);
> +#endif
> Index: linux-2.6.26/kernel/timer.c
> ===================================================================
> --- linux-2.6.26.orig/kernel/timer.c 2008-09-15 08:14:40.000000000 +0000
> +++ linux-2.6.26/kernel/timer.c 2008-09-15 11:22:06.000000000 +0000
> @@ -37,6 +37,7 @@
> #include <linux/delay.h>
> #include <linux/tick.h>
> #include <linux/kallsyms.h>
> +#include <linux/timer.h>
>
> #include <asm/uaccess.h>
> #include <asm/unistd.h>
> @@ -87,8 +88,9 @@
> * the new flag to indicate whether the timer is deferrable
> */
> #define TBASE_DEFERRABLE_FLAG (0x1)
> +#define TBASE_PINNED_FLAG (0x2)
>
> -/* Functions below help us manage 'deferrable' flag */
> +/* Functions below help us manage 'deferrable' flag and 'cpu-pinned-timer' flag */
> static inline unsigned int tbase_get_deferrable(struct tvec_base *base)
> {
> return ((unsigned int)(unsigned long)base & TBASE_DEFERRABLE_FLAG);
> @@ -96,7 +98,7 @@
>
> static inline struct tvec_base *tbase_get_base(struct tvec_base *base)
> {
> - return ((struct tvec_base *)((unsigned long)base & ~TBASE_DEFERRABLE_FLAG));
> + return (struct tvec_base *)((unsigned long)base & ~TBASE_DEFERRABLE_FLAG & ~TBASE_PINNED_FLAG);
> }
I'm pretty sure this line is too long.
> static inline void timer_set_deferrable(struct timer_list *timer)
> @@ -105,11 +107,21 @@
> TBASE_DEFERRABLE_FLAG));
> }
>
> +static inline unsigned int tbase_get_pinned(struct tvec_base *base)
> +{
> + return ((unsigned int)(unsigned long)base & TBASE_PINNED_FLAG);
> +}
Why explicitly cast to unsigned int?
> static inline void
> timer_set_base(struct timer_list *timer, struct tvec_base *new_base)
> {
> timer->base = (struct tvec_base *)((unsigned long)(new_base) |
> - tbase_get_deferrable(timer->base));
> + tbase_get_deferrable(timer->base) | tbase_get_pinned(timer->base));
> +}
> +
> +static inline void timer_set_pinned(struct timer_list *timer)
> +{
> + timer->base = ((struct tvec_base *)((unsigned long)(timer->base) | TBASE_PINNED_FLAG));
> }
<80 ?
> /**
> @@ -540,6 +552,12 @@
>
> new_base = __get_cpu_var(tvec_bases);
>
> + #ifdef CONFIG_TIMER_MIGRATION
> + if (__get_cpu_var(enable_timer_migration) && !tbase_get_pinned(timer->base)) {
> + new_base = per_cpu(tvec_bases, 0);
> + }
> + #endif
We don't indent preprocessor directives like that, also we don't use
braces on single statement blocks.
> if (base != new_base) {
> /*
> * We are trying to schedule the timer on the local CPU.
> @@ -579,6 +597,7 @@
> struct tvec_base *base = per_cpu(tvec_bases, cpu);
> unsigned long flags;
>
> + timer_set_pinned(timer);
> timer_stats_timer_set_start_info(timer);
> BUG_ON(timer_pending(timer) || !timer->function);
> spin_lock_irqsave(&base->lock, flags);
> Index: linux-2.6.26/kernel/hrtimer.c
> ===================================================================
> --- linux-2.6.26.orig/kernel/hrtimer.c 2008-09-15 08:14:40.000000000 +0000
> +++ linux-2.6.26/kernel/hrtimer.c 2008-09-15 11:17:19.000000000 +0000
> @@ -200,6 +200,12 @@
> struct hrtimer_cpu_base *new_cpu_base;
>
> new_cpu_base = &__get_cpu_var(hrtimer_bases);
> +
> + #ifdef CONFIG_TIMER_MIGRATION
> + if (__get_cpu_var(enable_timer_migration))
> + new_cpu_base = &per_cpu(hrtimer_bases, 0);
> + #endif
idem
and NAK - this will actually break stuff.
> new_base = &new_cpu_base->clock_base[base->index];
>
> if (base != new_base) {
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