[PATCH] x86/platform/uv/BAU: disable BAU on single hub configurations

From	Andrew Banman <abanman@hpe.com>
Newsgroups	linux.kernel
Subject	[PATCH] x86/platform/uv/BAU: disable BAU on single hub configurations
Date	2017-07-19 00:10 +0200
Message-ID	<u4IQN-86Q-7@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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The BAU confers no benefit to a UV system running with only one hub/socket.
Permanently disable the BAU driver if there are less than two hubs online
to avoid BAU overhead. We have observed failed boots on single-socket UV4
systems caused by BAU that are avoided with this patch.

Signed-off-by: Andrew Banman <abanman@hpe.com>
Acked-by: Russ Anderson <rja@hpe.com>
Acked-by: Mike Travis <mike.travis@hpe.com>
---
 arch/x86/platform/uv/tlb_uv.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
index 2511a28..88216cc 100644
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -2251,6 +2251,12 @@ static int __init uv_bau_init(void)
 	}
 
 	nuvhubs = uv_num_possible_blades();
+	if (nuvhubs < 2) {
+		pr_crit("UV: BAU disabled - insufficient hub count\n");
+		set_bau_off();
+		nobau_perm = 1;
+		return 0;
+	}
 
 	uv_base_pnode = 0x7fffffff;
 	for (uvhub = 0; uvhub < nuvhubs; uvhub++) {
-- 
1.8.2.1

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[PATCH] x86/platform/uv/BAU: disable BAU on single hub configurations Andrew Banman <abanman@hpe.com> - 2017-07-19 00:10 +0200
  Re: [PATCH] x86/platform/uv/BAU: disable BAU on single hub  configurations Ingo Molnar <mingo@kernel.org> - 2017-07-20 13:50 +0200
    Re: [PATCH] x86/platform/uv/BAU: disable BAU on single hub  configurations Andrew Banman <abanman@hpe.com> - 2017-07-20 21:00 +0200
  [PATCH v2] x86/platform/uv/BAU: disable BAU on single hub configurations Andrew Banman <abanman@hpe.com> - 2017-07-21 00:10 +0200
    [tip:x86/urgent] x86/platform/uv/BAU: Disable BAU on single hub  configurations tip-bot for Andrew Banman <tipbot@zytor.com> - 2017-07-21 11:50 +0200

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