[PATCH] mlx5: avoid 64-bit division

[PATCH] mlx5: avoid 64-bit division

[Michal Kubecek]

Commit 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
breaks i386 build by introducing three 64-bit divisions. As the divisor
is MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace
the division with bit operations.

Fixes: 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
---
 drivers/infiniband/hw/mlx5/cmd.c  | 9 +++++++--
 drivers/infiniband/hw/mlx5/main.c | 2 +-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/cmd.c b/drivers/infiniband/hw/mlx5/cmd.c
index e3ec79b8f7f5..6c8645033102 100644
--- a/drivers/infiniband/hw/mlx5/cmd.c
+++ b/drivers/infiniband/hw/mlx5/cmd.c
@@ -190,12 +190,12 @@ int mlx5_cmd_alloc_sw_icm(struct mlx5_dm *dm, int type, u64 length,
 			  u16 uid, phys_addr_t *addr, u32 *obj_id)
 {
 	struct mlx5_core_dev *dev = dm->dev;
-	u32 num_blocks = DIV_ROUND_UP(length, MLX5_SW_ICM_BLOCK_SIZE(dev));
 	u32 out[MLX5_ST_SZ_DW(general_obj_out_cmd_hdr)] = {};
 	u32 in[MLX5_ST_SZ_DW(create_sw_icm_in)] = {};
 	unsigned long *block_map;
 	u64 icm_start_addr;
 	u32 log_icm_size;
+	u32 num_blocks;
 	u32 max_blocks;
 	u64 block_idx;
 	void *sw_icm;
@@ -224,6 +224,8 @@ int mlx5_cmd_alloc_sw_icm(struct mlx5_dm *dm, int type, u64 length,
 		return -EINVAL;
 	}
 
+	num_blocks = (length + MLX5_SW_ICM_BLOCK_SIZE(dev) - 1) >>
+		     MLX5_LOG_SW_ICM_BLOCK_SIZE(dev);
 	max_blocks = BIT(log_icm_size - MLX5_LOG_SW_ICM_BLOCK_SIZE(dev));
 	spin_lock(&dm->lock);
 	block_idx = bitmap_find_next_zero_area(block_map,
@@ -266,13 +268,16 @@ int mlx5_cmd_dealloc_sw_icm(struct mlx5_dm *dm, int type, u64 length,
 			    u16 uid, phys_addr_t addr, u32 obj_id)
 {
 	struct mlx5_core_dev *dev = dm->dev;
-	u32 num_blocks = DIV_ROUND_UP(length, MLX5_SW_ICM_BLOCK_SIZE(dev));
 	u32 out[MLX5_ST_SZ_DW(general_obj_out_cmd_hdr)] = {};
 	u32 in[MLX5_ST_SZ_DW(general_obj_in_cmd_hdr)] = {};
 	unsigned long *block_map;
+	u32 num_blocks;
 	u64 start_idx;
 	int err;
 
+	num_blocks = (length + MLX5_SW_ICM_BLOCK_SIZE(dev) - 1) >>
+		     MLX5_LOG_SW_ICM_BLOCK_SIZE(dev);
+
 	switch (type) {
 	case MLX5_IB_UAPI_DM_TYPE_STEERING_SW_ICM:
 		start_idx =
diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index abac70ad5c7c..340290b883fe 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -2344,7 +2344,7 @@ static int handle_alloc_dm_sw_icm(struct ib_ucontext *ctx,
 	/* Allocation size must a multiple of the basic block size
 	 * and a power of 2.
 	 */
-	act_size = roundup(attr->length, MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));
+	act_size = round_up(attr->length, MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));
 	act_size = roundup_pow_of_two(act_size);
 
 	dm->size = act_size;
-- 
2.21.0

Re: [PATCH] mlx5: avoid 64-bit division

[Leon Romanovsky]

On Mon, May 20, 2019 at 01:19:02PM +0200, Michal Kubecek wrote:
> Commit 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
> breaks i386 build by introducing three 64-bit divisions. As the divisor
> is MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace
> the division with bit operations.

Interesting, we tried to solve it differently.
I added it to our regression to be on the same side.

Thanks

Re: [PATCH] mlx5: avoid 64-bit division

[Jason Gunthorpe]

On Mon, May 20, 2019 at 01:19:02PM +0200, Michal Kubecek wrote:
> Commit 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
> breaks i386 build by introducing three 64-bit divisions. As the divisor
> is MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace
> the division with bit operations.
> 
> Fixes: 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
> Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
>  drivers/infiniband/hw/mlx5/cmd.c  | 9 +++++++--
>  drivers/infiniband/hw/mlx5/main.c | 2 +-
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/cmd.c b/drivers/infiniband/hw/mlx5/cmd.c
> index e3ec79b8f7f5..6c8645033102 100644
> +++ b/drivers/infiniband/hw/mlx5/cmd.c
> @@ -190,12 +190,12 @@ int mlx5_cmd_alloc_sw_icm(struct mlx5_dm *dm, int type, u64 length,
>  			  u16 uid, phys_addr_t *addr, u32 *obj_id)
>  {
>  	struct mlx5_core_dev *dev = dm->dev;
> -	u32 num_blocks = DIV_ROUND_UP(length, MLX5_SW_ICM_BLOCK_SIZE(dev));
>  	u32 out[MLX5_ST_SZ_DW(general_obj_out_cmd_hdr)] = {};
>  	u32 in[MLX5_ST_SZ_DW(create_sw_icm_in)] = {};
>  	unsigned long *block_map;
>  	u64 icm_start_addr;
>  	u32 log_icm_size;
> +	u32 num_blocks;
>  	u32 max_blocks;
>  	u64 block_idx;
>  	void *sw_icm;
> @@ -224,6 +224,8 @@ int mlx5_cmd_alloc_sw_icm(struct mlx5_dm *dm, int type, u64 length,
>  		return -EINVAL;
>  	}
>  
> +	num_blocks = (length + MLX5_SW_ICM_BLOCK_SIZE(dev) - 1) >>
> +		     MLX5_LOG_SW_ICM_BLOCK_SIZE(dev);
>  	max_blocks = BIT(log_icm_size - MLX5_LOG_SW_ICM_BLOCK_SIZE(dev));
>  	spin_lock(&dm->lock);
>  	block_idx = bitmap_find_next_zero_area(block_map,
> @@ -266,13 +268,16 @@ int mlx5_cmd_dealloc_sw_icm(struct mlx5_dm *dm, int type, u64 length,
>  			    u16 uid, phys_addr_t addr, u32 obj_id)
>  {
>  	struct mlx5_core_dev *dev = dm->dev;
> -	u32 num_blocks = DIV_ROUND_UP(length, MLX5_SW_ICM_BLOCK_SIZE(dev));
>  	u32 out[MLX5_ST_SZ_DW(general_obj_out_cmd_hdr)] = {};
>  	u32 in[MLX5_ST_SZ_DW(general_obj_in_cmd_hdr)] = {};
>  	unsigned long *block_map;
> +	u32 num_blocks;
>  	u64 start_idx;
>  	int err;
>  
> +	num_blocks = (length + MLX5_SW_ICM_BLOCK_SIZE(dev) - 1) >>
> +		     MLX5_LOG_SW_ICM_BLOCK_SIZE(dev);
> +
>  	switch (type) {
>  	case MLX5_IB_UAPI_DM_TYPE_STEERING_SW_ICM:
>  		start_idx =
> diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> index abac70ad5c7c..340290b883fe 100644
> +++ b/drivers/infiniband/hw/mlx5/main.c
> @@ -2344,7 +2344,7 @@ static int handle_alloc_dm_sw_icm(struct ib_ucontext *ctx,
>  	/* Allocation size must a multiple of the basic block size
>  	 * and a power of 2.
>  	 */
> -	act_size = roundup(attr->length, MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));
> +	act_size = round_up(attr->length, MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));
>  	act_size = roundup_pow_of_two(act_size);

It is kind of weird that we have round_up and the bitshift
version.. None of this is performance critical so why not just use
round_up everywhere?

Ariel, it is true MLX5_SW_ICM_BLOCK_SIZE will always be a power of
two?

Jason

Re: [PATCH] mlx5: avoid 64-bit division

[Michal Kubecek]

On Mon, May 27, 2019 at 03:15:34PM -0300, Jason Gunthorpe wrote:
> On Mon, May 20, 2019 at 01:19:02PM +0200, Michal Kubecek wrote:
> > diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> > index abac70ad5c7c..340290b883fe 100644
> > +++ b/drivers/infiniband/hw/mlx5/main.c
> > @@ -2344,7 +2344,7 @@ static int handle_alloc_dm_sw_icm(struct ib_ucontext *ctx,
> >  	/* Allocation size must a multiple of the basic block size
> >  	 * and a power of 2.
> >  	 */
> > -	act_size = roundup(attr->length, MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));
> > +	act_size = round_up(attr->length, MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));
> >  	act_size = roundup_pow_of_two(act_size);
> 
> It is kind of weird that we have round_up and the bitshift
> version.. None of this is performance critical so why not just use
> round_up everywhere?
> 
> Ariel, it is true MLX5_SW_ICM_BLOCK_SIZE will always be a power of
> two?

If it weren't, the requirements from the comment above could never be
satisfied as a power of two can only be a multiple of another power of
two. Which also means that what the code above does is in fact
equivalent to

	act_size = max_t(u64, roundup_pow_of_two(attr->length),
			 MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));

or

	act_size = roundup_pow_of_two(max_t(u64, attr->length,
					    MLX5_SW_ICM_BLOCK_SIZE(dm_db->dev));

Michal Kubecek

Re: [PATCH] mlx5: avoid 64-bit division

[Leon Romanovsky]

On Mon, May 20, 2019 at 02:28:35PM +0300, Leon Romanovsky wrote:
> On Mon, May 20, 2019 at 01:19:02PM +0200, Michal Kubecek wrote:
> > Commit 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
> > breaks i386 build by introducing three 64-bit divisions. As the divisor
> > is MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace
> > the division with bit operations.
>
> Interesting, we tried to solve it differently.
> I added it to our regression to be on the same side.

This patch works for us.

Thanks,
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>

Re: [PATCH] mlx5: avoid 64-bit division

[Ariel Levkovich]

   On Mon, May 20, 2019 at 02:28:35PM +0300, Leon Romanovsky wrote:
    > > On Mon, May 20, 2019 at 01:19:02PM +0200, Michal Kubecek wrote:
    > > > Commit 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
    > > > breaks i386 build by introducing three 64-bit divisions. As the divisor
    > > > is MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace
    > > > the division with bit operations.
    > >
    > > Interesting, we tried to solve it differently.
    > > I added it to our regression to be on the same side.
    
    > This patch works for us.
    
   Yes, this value is guaranteed to be a power of 2.  We safely use round_up() instead as suggested in the patch.

Re: [PATCH] mlx5: avoid 64-bit division

[Jason Gunthorpe]

On Mon, May 20, 2019 at 01:19:02PM +0200, Michal Kubecek wrote:
> Commit 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
> breaks i386 build by introducing three 64-bit divisions. As the divisor
> is MLX5_SW_ICM_BLOCK_SIZE() which is always a power of 2, we can replace
> the division with bit operations.
> 
> Fixes: 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")
> Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
> Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
> ---
>  drivers/infiniband/hw/mlx5/cmd.c  | 9 +++++++--
>  drivers/infiniband/hw/mlx5/main.c | 2 +-
>  2 files changed, 8 insertions(+), 3 deletions(-)

Applied to for-rc, thanks

Jason