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From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 30 Jan 2017 09:41:21 +0100
Subject: [PATCH] x86/mm/cpa: avoid wbinvd() for PREEMPT
Although wbinvd() is faster than flushing many individual pages, it
blocks the memory bus for "long" periods of time (>100us), thus
directly causing unusually large latencies on all CPUs, regardless
of any CPU isolation features that may be active.
For 1024 pages, flushing those pages individually can take up to
2200us, but the task remains fully preemptible during that time.
Cc: stable-rt@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/x86/mm/pageattr.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -214,7 +214,15 @@ static void cpa_flush_array(unsigned lon
int in_flags, struct page **pages)
{
unsigned int i, level;
+#ifdef CONFIG_PREEMPT
+ /*
+ * Avoid wbinvd() because it causes latencies on all CPUs,
+ * regardless of any CPU isolation that may be in effect.
+ */
+ unsigned long do_wbinvd = 0;
+#else
unsigned long do_wbinvd = cache && numpages >= 1024; /* 4M threshold */
+#endif
BUG_ON(irqs_disabled());
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