linux-kernel - [PATCH v2 2/2] powerpc: pci-ioda: Optimize pnv_ioda_pick_m64

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Message-ID: <20250811165130.37552-3-yury.norov@gmail.com>
Date: Mon, 11 Aug 2025 12:51:28 -0400
From: Yury Norov <yury.norov@...il.com>
To: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Barrat <fbarrat@...ux.ibm.com>,
	Andrew Donnellan <ajd@...ux.ibm.com>,
	Yury Norov <yury.norov@...il.com>,
	linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] powerpc: pci-ioda: Optimize pnv_ioda_pick_m64_pe()

From: "Yury Norov (NVIDIA)" <yury.norov@...il.com>

bitmap_empty() in pnv_ioda_pick_m64_pe() is O(N) and useless because
the following find_next_bit() does the same work.

Drop it, and while there replace a while() loop with the dedicated
for_each_set_bit().

Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
---
 arch/powerpc/platforms/powernv/pci-ioda.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index e2b0132fb6a1..325197ac19e5 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -295,7 +295,7 @@ static struct pnv_ioda_pe *pnv_ioda_pick_m64_pe(struct pci_bus *bus, bool all)
 	unsigned long *pe_alloc __free(bitmap) = NULL;
 	struct pnv_phb *phb = pci_bus_to_pnvhb(bus);
 	struct pnv_ioda_pe *master_pe, *pe;
-	int i;
+	unsigned int i;
 
 	/* Root bus shouldn't use M64 */
 	if (pci_is_root_bus(bus))
@@ -311,23 +311,16 @@ static struct pnv_ioda_pe *pnv_ioda_pick_m64_pe(struct pci_bus *bus, bool all)
 	/* Figure out reserved PE numbers by the PE */
 	pnv_ioda_reserve_m64_pe(bus, pe_alloc, all);
 
-	/*
-	 * the current bus might not own M64 window and that's all
-	 * contributed by its child buses. For the case, we needn't
-	 * pick M64 dependent PE#.
-	 */
-	if (bitmap_empty(pe_alloc, phb->ioda.total_pe_num)) {
-		return NULL;
-	}
-
 	/*
 	 * Figure out the master PE and put all slave PEs to master
 	 * PE's list to form compound PE.
+	 *
+	 * The current bus might not own M64 window and that's all
+	 * contributed by its child buses. For the case, we needn't
+	 * pick M64 dependent PE#.
 	 */
 	master_pe = NULL;
-	i = -1;
-	while ((i = find_next_bit(pe_alloc, phb->ioda.total_pe_num, i + 1)) <
-		phb->ioda.total_pe_num) {
+	for_each_set_bit(i, pe_alloc, phb->ioda.total_pe_num) {
 		pe = &phb->ioda.pe_array[i];
 
 		phb->ioda.m64_segmap[pe->pe_number] = pe->pe_number;
-- 
2.43.0