45 lines
1.5 KiB
Diff
45 lines
1.5 KiB
Diff
From c88e41f659f6a96f5feca2c02abbc7b078c5a7bc Mon Sep 17 00:00:00 2001
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From: John Ogness <john.ogness@linutronix.de>
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Date: Mon, 30 Jan 2017 09:41:21 +0100
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Subject: [PATCH 044/365] x86/mm/cpa: avoid wbinvd() for PREEMPT
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Although wbinvd() is faster than flushing many individual pages, it
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blocks the memory bus for "long" periods of time (>100us), thus
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directly causing unusually large latencies on all CPUs, regardless
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of any CPU isolation features that may be active.
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For 1024 pages, flushing those pages individually can take up to
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2200us, but the task remains fully preemptible during that time.
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Cc: stable-rt@vger.kernel.org
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Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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arch/x86/mm/pageattr.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
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index 1271bc9fa3c6..83d9fde74c75 100644
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--- a/arch/x86/mm/pageattr.c
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+++ b/arch/x86/mm/pageattr.c
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@@ -215,7 +215,15 @@ static void cpa_flush_array(unsigned long *start, int numpages, int cache,
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int in_flags, struct page **pages)
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{
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unsigned int i, level;
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+#ifdef CONFIG_PREEMPT
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+ /*
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+ * Avoid wbinvd() because it causes latencies on all CPUs,
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+ * regardless of any CPU isolation that may be in effect.
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+ */
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+ unsigned long do_wbinvd = 0;
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+#else
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unsigned long do_wbinvd = cache && numpages >= 1024; /* 4M threshold */
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+#endif
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BUG_ON(irqs_disabled());
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--
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2.28.0
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