linux-kernel - [PATCH] RISC-V: Do not issue remote fences until smp is available

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Message-Id: <20221028231929.347918-1-atishp@rivosinc.com>
Date:   Fri, 28 Oct 2022 16:19:29 -0700
From:   Atish Patra <atishp@...osinc.com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atishp@...osinc.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Anup Patel <anup@...infault.org>,
        Damien Le Moal <damien.lemoal@....com>,
        devicetree@...r.kernel.org, Jisheng Zhang <jszhang@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: [PATCH] RISC-V: Do not issue remote fences until smp is available

It is useless to issue remote fences if there is a single core
available. It becomes a bottleneck for sbi based rfences where
we will be making those ECALLs for no reason. Early code patching
because of static calls end up in this path.

Signed-off-by: Atish Patra <atishp@...osinc.com>
---
 arch/riscv/mm/cacheflush.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
index f10cb47eac3a..7fafc8c26505 100644
--- a/arch/riscv/mm/cacheflush.c
+++ b/arch/riscv/mm/cacheflush.c
@@ -19,6 +19,10 @@ void flush_icache_all(void)
 {
 	local_flush_icache_all();
 
+	/* No need to issue remote fence if only 1 cpu is online */
+	if (num_online_cpus() == 1)
+		return;
+
 	if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
 		sbi_remote_fence_i(NULL);
 	else
-- 
2.34.1