RE: [PATCH] SN2 user-MMIO CPU migration

Chen, Kenneth W
2006-01-25T09:04:01Z

Brent Casavant wrote on Tuesday, January 24, 2006 4:11 PM
> > Brent Casavant wrote on Tuesday, January 24, 2006 3:29 PM
> > > Take 4. Moved "really migrated?" check as late as possible in
> > > __switch_task(), and moved thread_info last_cpu field closer to
> > > flags and cpu fields. Some nomenclature changes as well.
> >
> > I think you should seriously consider my other proposal :-)
>
> Well... if Ingo is amenable to the arch hook in the scheduler, I'm
> OK with changing directions. Again. :-)

Hmm, I'm not proposing for arch hook at all.

> The arch hook would be a lot simpler this time -- simply setting
> a flag instead of performing the PIO write drain. Not sure if
> that's enough to argue in favor of the hook or not.
>
> Truth be told, I have no strong preference either way. I'd just
> like to break out of this Brownian motion. :-)

This is the "what the heck is he talking about?" patch, on top of
"take 4" patch:

---
Optimize platform_migrate(): call platform specific vector only
if machine requires it.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

--- linus-2.6.git/include/asm-ia64/processor.h.orig 2006-01-21 10:58:06.000000000 -0800
+++ linus-2.6.git/include/asm-ia64/processor.h 2006-01-25 01:09:34.169421315 -0800
@@ -50,7 +50,7 @@
#define IA64_THREAD_PM_VALID (__IA64_UL(1) << 2) /* performance registers valid? */
#define IA64_THREAD_UAC_NOPRINT (__IA64_UL(1) << 3) /* don't log unaligned accesses */
#define IA64_THREAD_UAC_SIGBUS (__IA64_UL(1) << 4) /* generate SIGBUS on unaligned acc. */
- /* bit 5 is currently unused */
+#define IA64_THREAD_MIGRATION (__IA64_UL(1) << 5) /* require migration sync at ctx sw */
#define IA64_THREAD_FPEMU_NOPRINT (__IA64_UL(1) << 6) /* don't log any fpswa faults */
#define IA64_THREAD_FPEMU_SIGFPE (__IA64_UL(1) << 7) /* send a SIGFPE for fpswa faults */

--- linus-2.6.git/include/asm-ia64/system.h.orig 2006-01-25 01:14:07.661605464 -0800
+++ linus-2.6.git/include/asm-ia64/system.h 2006-01-25 01:17:36.173321660 -0800
@@ -221,23 +221,12 @@ extern void ia64_load_extra (struct task
((t)->thread.flags & (IA64_THREAD_DBG_VALID|IA64_THREAD_PM_VALID) \
|| IS_IA32_PROCESS(task_pt_regs(t)) || PERFMON_IS_SYSWIDE())

-#ifdef CONFIG_SMP
-# define arch_migrate(task) \
- if (task_cpu(task) != task_thread_info(task)->last_cpu) { \
- platform_migrate(task); \
- task_thread_info(task)->last_cpu = task_cpu(task); \
- }
-#else
-# define arch_migrate(task) do { } while(0)
-#endif
-
#define __switch_to(prev,next,last) do { \
if (IA64_HAS_EXTRA_STATE(prev)) \
ia64_save_extra(prev); \
if (IA64_HAS_EXTRA_STATE(next)) \
ia64_load_extra(next); \
ia64_psr(task_pt_regs(next))->dfh = !ia64_is_local_fpu_owner(next); \
- arch_migrate(next); \
(last) = ia64_switch_to((next)); \
} while (0)

@@ -255,6 +244,8 @@ extern void ia64_load_extra (struct task
__ia64_save_fpu((prev)->thread.fph); \
} \
__switch_to(prev, next, last); \
+ if (unlikely((next)->thread.flags & IA64_THREAD_MIGRATION)) \
+ platform_migrate(next); \
} while (0)
#else
# define switch_to(prev,next,last) __switch_to(prev, next, last)
--- linus-2.6.git/arch/ia64/sn/kernel/sn2/sn2_smp.c.orig 2006-01-25 01:13:56.322738416 -0800
+++ linus-2.6.git/arch/ia64/sn/kernel/sn2/sn2_smp.c 2006-01-25 01:19:27.169414050 -0800
@@ -184,9 +184,13 @@ void sn_migrate(struct task_struct *task
volatile unsigned long *adr = last_pda->pio_write_status_addr;
unsigned long val = last_pda->pio_write_status_val;

+ if (task_cpu(task) = task_thread_info(task)->last_cpu)
+ return;
+
/* Drain PIO writes from old CPU's Shub */
while ((*adr & SH_PIO_WRITE_STATUS_PENDING_WRITE_COUNT_MASK) != val)
cpu_relax();
+ task_thread_info(task)->last_cpu = task_cpu(task);
}

void sn_tlb_migrate_finish(struct mm_struct *mm)
--- linus-2.6.git/arch/ia64/sn/kernel/setup.c.orig 2006-01-25 01:02:30.830559313 -0800
+++ linus-2.6.git/arch/ia64/sn/kernel/setup.c 2006-01-25 01:09:57.794421025 -0800
@@ -496,6 +496,7 @@ void __init sn_setup(char **cmdline_p)
* for sn.
*/
pm_power_off = ia64_sn_power_down;
+ current->thread.flags |= IA64_THREAD_MIGRATION;
}

/**