linux-kernel - [PATCH v5 05/13] riscv: Only send remote fences when some other CPU is online

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Date: Thu, 29 Feb 2024 15:21:46 -0800
From: Samuel Holland <samuel.holland@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>,
	linux-riscv@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Jisheng Zhang <jszhang@...nel.org>,
	Yunhui Cui <cuiyunhui@...edance.com>,
	Samuel Holland <samuel.holland@...ive.com>
Subject: [PATCH v5 05/13] riscv: Only send remote fences when some other CPU is online

If no other CPU is online, a local cache or TLB flush is sufficient.
These checks can be constant-folded when SMP is disabled.

Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

(no changes since v4)

Changes in v4:
 - New patch for v4

 arch/riscv/mm/cacheflush.c | 4 +++-
 arch/riscv/mm/tlbflush.c   | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
index 47c485bc7df0..f7933ae88a55 100644
--- a/arch/riscv/mm/cacheflush.c
+++ b/arch/riscv/mm/cacheflush.c
@@ -21,7 +21,9 @@ void flush_icache_all(void)
 {
 	local_flush_icache_all();
 
-	if (riscv_use_sbi_for_rfence())
+	if (num_online_cpus() < 2)
+		return;
+	else if (riscv_use_sbi_for_rfence())
 		sbi_remote_fence_i(NULL);
 	else
 		on_each_cpu(ipi_remote_fence_i, NULL, 1);
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 8cdb082f00ca..69402c260a89 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -78,7 +78,9 @@ static void __ipi_flush_tlb_all(void *info)
 
 void flush_tlb_all(void)
 {
-	if (riscv_use_sbi_for_rfence())
+	if (num_online_cpus() < 2)
+		local_flush_tlb_all();
+	else if (riscv_use_sbi_for_rfence())
 		sbi_remote_sfence_vma_asid(NULL, 0, FLUSH_TLB_MAX_SIZE, FLUSH_TLB_NO_ASID);
 	else
 		on_each_cpu(__ipi_flush_tlb_all, NULL, 1);
-- 
2.43.1