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Date: Tue, 17 Feb 2015 14:02:49 +0100
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>,
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        John Kacur <jkacur@redhat.com>, Clark Williams <williams@redhat.com>
Subject: Re: 3.14.23-rt20 - x86, UV: raw_spinlock conversion
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* Mike Galbraith | 2014-11-02 08:31:37 [+0100]:

>Shrug.  Lots of hobbyists have a beast in their basement, right?

I can take this as is if you want.

>--- a/arch/x86/platform/uv/uv_time.c
>+++ b/arch/x86/platform/uv/uv_time.c
>@@ -300,13 +300,18 @@ static int uv_rtc_unset_timer(int cpu, i
> static cycle_t uv_read_rtc(struct clocksource *cs)
> {
> 	unsigned long offset;
>+	cycle_t cycles;
> 
>+	migrate_disable();
> 	if (uv_get_min_hub_revision_id() == 1)
> 		offset = 0;
> 	else
> 		offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;
> 
>-	return (cycle_t)uv_read_local_mmr(UVH_RTC | offset);
>+	cycles = (cycle_t)uv_read_local_mmr(UVH_RTC | offset);
>+	migrate_enable();
>+
>+	return cycles;
> }

but do you really want a migrate_disable() in here? The only problem I
can imagine is that you switch CPUs between uv_blade_processor_id()
and the actual read. I recommend preempt_disable() and sending this
upstream as well since it is not limited to -RT.

Sebastian