Re: [PATCH] i386 No Idle HZ aka dynticks 051217

[Con Kolivas <kernel@kolivas.org>]

On Monday 19 December 2005 02:22, Con Kolivas wrote:
> On Monday 19 December 2005 02:19, Con Kolivas wrote:
> > Here is yet another updated version of the dynticks code.
> >
> > Changes:
> >
> > Numerous cleanups, microoptimisations and locking improvements.
> >
> > One bugfix for the next tick accounting used in early_dyn_reprogram
> >
> > I've yet to find the cause for grossly high cpu accounting on SMP. I'd
> > appreciate any help in this area as it's the last showstopper for this
> > code.
> >
> > Obvious power savings are evident on uniprocessor now in on/off
> > comparisons using pmstats.
>
> That would be dynticks-051218 I mean, sorry.

Oops, wrong locking order may cause a livelock so this patch will be needed.

Uploaded a 051218-1 patch to website with this bug fix.

http://ck.kolivas.org/patches/dyn-ticks/

Cheers,
Con

---
 arch/i386/kernel/dyn-tick.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

Index: linux-2.6.15-rc5-dt/arch/i386/kernel/dyn-tick.c
===================================================================
--- linux-2.6.15-rc5-dt.orig/arch/i386/kernel/dyn-tick.c
+++ linux-2.6.15-rc5-dt/arch/i386/kernel/dyn-tick.c
@@ -126,16 +126,14 @@ static void do_dyn_tick_interrupt(struct
 {
 	int cpu = smp_processor_id();
 
+	write_seqlock(&xtime_lock);
 	spin_lock(&dyn_tick->lock);
 	if (cpus_equal(nohz_cpu_mask, cpu_online_map)) {
 		/* All were sleeping, recover jiffies */
 		int lost = cur_timer->mark_offset();
 
-		if (lost && in_irq()) {
-			write_seqlock(&xtime_lock);
+		if (lost && in_irq())
 			do_timer(regs);
-			write_sequnlock(&xtime_lock);
-		}
 		if (dyntick_using_lapic()) {
 			enable_pit_timer();
 			if (unlikely(lost > DYN_TICK_MAX_SKIP + 1))
@@ -145,6 +143,7 @@ static void do_dyn_tick_interrupt(struct
 	}
 	clear_nohz_cpu(cpu);
 	spin_unlock(&dyn_tick->lock);
+	write_sequnlock(&xtime_lock);
 
 	/* Make sure we don't miss the next timer tick */
 	dyn_early_reprogram(1);

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