linux-kernel - [PATCH rdma] IB/mlx5: Optimize u64 division on 32-bit arches

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Date:   Mon, 17 Feb 2020 10:36:29 +0300
From:   Alexander Lobakin <alobakin@...nk.ru>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Alexander Lobakin <alobakin@...nk.ru>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH rdma] IB/mlx5: Optimize u64 division on 32-bit arches

Commit f164be8c0366 ("IB/mlx5: Extend caps stage to handle VAR
capabilities") introduced a straight "/" division of the u64
variable "bar_size".
This was fixed with commit 685eff513183 ("IB/mlx5: Use div64_u64
for num_var_hw_entries calculation"). However, div64_u64() is
redundant here as mlx5_var_table::stride_size is of type u32.
Make the actual code way more optimized on 32-bit kernels using
div_u64() and fix 80 chars break-through by the way.

Fixes: 685eff513183 ("IB/mlx5: Use div64_u64 for num_var_hw_entries
calculation")
Signed-off-by: Alexander Lobakin <alobakin@...nk.ru>
---
 drivers/infiniband/hw/mlx5/main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index e4bcfa81b70a..026391e4ceb4 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -6545,7 +6545,8 @@ static int mlx5_ib_init_var_table(struct mlx5_ib_dev *dev)
 					doorbell_bar_offset);
 	bar_size = (1ULL << log_doorbell_bar_size) * 4096;
 	var_table->stride_size = 1ULL << log_doorbell_stride;
-	var_table->num_var_hw_entries = div64_u64(bar_size, var_table->stride_size);
+	var_table->num_var_hw_entries = div_u64(bar_size,
+						var_table->stride_size);
 	mutex_init(&var_table->bitmap_lock);
 	var_table->bitmap = bitmap_zalloc(var_table->num_var_hw_entries,
 					  GFP_KERNEL);
-- 
2.25.0