linux-kernel - [PATCH 2/3] arm64, mm: Use flush_tlb_all_local() in flush

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Date:	Sat, 11 Jul 2015 13:25:22 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	linux-arm-kernel@...ts.infradead.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>
Cc:	linux-kernel@...r.kernel.org, Robert Richter <rrichter@...ium.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Daney <david.daney@...ium.com>
Subject: [PATCH 2/3] arm64, mm: Use flush_tlb_all_local() in flush_context().

From: David Daney <david.daney@...ium.com>

When CONFIG_SMP, we end up calling flush_context() on each CPU
(indirectly) from __new_context().  Because of this, doing a broadcast
TLB invalidate is overkill, as all CPUs will be doing a local
invalidation.

Change the scope of the TLB invalidation operation to be local,
resulting in nr_cpus invalidations, rather than nr_cpus^2.

On CPUs with a large ASID space this operation is not often done.
But, when it is, this reduces the overhead.

Benchmarked "time make -j48" kernel build with and without the patch on
Cavium ThunderX system, one run to warm up the caches, and then five
runs measured:

original      with-patch
139.299s      139.0766s
S.D. 0.321    S.D. 0.159

Probably a little faster, but could be measurement noise.

Signed-off-by: David Daney <david.daney@...ium.com>
---
 arch/arm64/mm/context.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 76c1e6c..ab5b8d3 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -48,7 +48,7 @@ static void flush_context(void)
 {
 	/* set the reserved TTBR0 before flushing the TLB */
 	cpu_set_reserved_ttbr0();
-	flush_tlb_all();
+	flush_tlb_all_local();
 	if (icache_is_aivivt())
 		__flush_icache_all();
 }
-- 
1.9.1

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