2010-07-07 11:12:45 +00:00
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Date: Tue, 6 Jan 2009 10:27:41 -0600
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From: Dimitri Sivanich <sivanich@sgi.com>
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To: linux-ia64@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
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Greg KH <greg@kroah.com>
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Cc: linux-kernel@vger.kernel.org,
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Peter Zijlstra <peterz@infradead.org>,
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Gregory Haskins <ghaskins@novell.com>, Nick Piggin <npiggin@suse.de>,
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Tony Luck <tony.luck@gmail.com>, Robin Holt <holt@sgi.com>
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Subject: configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems
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Patch-mainline: not yet
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Turn on CONFIG_HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN.
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SGI Altix has unsynchronized itc clocks. This results in rq->clock
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occasionally being set to a time in the past by a remote cpu.
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Note that it is possible that this problem may exist for other ia64
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machines as well, based on the following comment for sched_clock() in
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arch/ia64/kernel/head.S:
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* Return a CPU-local timestamp in nano-seconds. This timestamp is
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* NOT synchronized across CPUs its return value must never be
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* compared against the values returned on another CPU. The usage in
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* kernel/sched.c ensures that.
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Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
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Signed-off-by: Gregory Haskins <ghaskins@novell.com>
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---
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arch/ia64/Kconfig | 1 +
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1 file changed, 1 insertion(+)
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--- a/arch/ia64/Kconfig
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+++ b/arch/ia64/Kconfig
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2011-04-19 20:09:59 +00:00
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@@ -548,6 +548,7 @@ config IA64_MC_ERR_INJECT
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2010-07-07 11:12:45 +00:00
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config SGI_SN
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def_bool y if (IA64_SGI_SN2 || IA64_GENERIC)
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+ select HAVE_UNSTABLE_SCHED_CLOCK
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config IA64_ESI
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bool "ESI (Extensible SAL Interface) support"
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