linux-kernel - Re: 3.14.23-rt20 - x86, UV: raw

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Message-ID: <20150217130249.GK26177@linutronix.de>
Date:	Tue, 17 Feb 2015 14:02:49 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	John Kacur <jkacur@...hat.com>,
	Clark Williams <williams@...hat.com>
Subject: Re: 3.14.23-rt20 - x86, UV: raw_spinlock conversion

* 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
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