diff mbox series

[net-next,1/7] dma: compile-out DMA sync op calls when not used

Message ID 20240126135456.704351-2-aleksander.lobakin@intel.com
State New
Headers
Series dma: skip calling no-op sync ops when possible |

Commit Message

Alexander Lobakin Jan. 26, 2024, 1:54 p.m. UTC 
  Some platforms do have DMA, but DMA there is always direct and coherent.
Currently, even on such platforms DMA sync operations are compiled and
called.
Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
either sync operations are needed or there is DMA ops or swiotlb
enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
depending on this symbol state and don't call sync ops when
dma_skip_sync() is true.
The change allows for future optimizations of DMA sync calls depending
on compile-time or runtime conditions.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 kernel/dma/Kconfig          |  4 ++
 include/linux/dma-mapping.h | 92 +++++++++++++++++++++++++------------
 kernel/dma/mapping.c        | 26 ++++++-----
 3 files changed, 81 insertions(+), 41 deletions(-)

Comments

Christoph Hellwig Jan. 29, 2024, 6:11 a.m. UTC | #1 
On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
> Some platforms do have DMA, but DMA there is always direct and coherent.
> Currently, even on such platforms DMA sync operations are compiled and
> called.
> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
> either sync operations are needed or there is DMA ops or swiotlb
> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
> depending on this symbol state and don't call sync ops when
> dma_skip_sync() is true.
> The change allows for future optimizations of DMA sync calls depending
> on compile-time or runtime conditions.

So the idea of compiling out the calls sounds fine to me.  But what
is the point of the extra indirection through the __-prefixed calls?

And if we need that (please document it in the commit log), please
make the wrappers proper inline functions and not macros.
Alexander Lobakin Jan. 29, 2024, 11:07 a.m. UTC | #2 
From: Christoph Hellwig <hch@lst.de>
Date: Mon, 29 Jan 2024 07:11:36 +0100

> On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
>> Some platforms do have DMA, but DMA there is always direct and coherent.
>> Currently, even on such platforms DMA sync operations are compiled and
>> called.
>> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
>> either sync operations are needed or there is DMA ops or swiotlb
>> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
>> depending on this symbol state and don't call sync ops when
>> dma_skip_sync() is true.
>> The change allows for future optimizations of DMA sync calls depending
>> on compile-time or runtime conditions.
> 
> So the idea of compiling out the calls sounds fine to me.  But what
> is the point of the extra indirection through the __-prefixed calls?

Because dma_sync_* ops are external functions, not inlines, and in the
next patch I'm adding a check there.

> 
> And if we need that (please document it in the commit log), please
> make the wrappers proper inline functions and not macros.

Thanks,
Olek
Robin Murphy Jan. 29, 2024, 12:15 p.m. UTC | #3 
On 2024-01-29 11:07 am, Alexander Lobakin wrote:
> From: Christoph Hellwig <hch@lst.de>
> Date: Mon, 29 Jan 2024 07:11:36 +0100
> 
>> On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
>>> Some platforms do have DMA, but DMA there is always direct and coherent.
>>> Currently, even on such platforms DMA sync operations are compiled and
>>> called.
>>> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
>>> either sync operations are needed or there is DMA ops or swiotlb
>>> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
>>> depending on this symbol state and don't call sync ops when
>>> dma_skip_sync() is true.
>>> The change allows for future optimizations of DMA sync calls depending
>>> on compile-time or runtime conditions.
>>
>> So the idea of compiling out the calls sounds fine to me.  But what
>> is the point of the extra indirection through the __-prefixed calls?
> 
> Because dma_sync_* ops are external functions, not inlines, and in the
> next patch I'm adding a check there.
> 
>>
>> And if we need that (please document it in the commit log), please
>> make the wrappers proper inline functions and not macros.

In fact those wrappers could perhaps subsume the existing stub 
definitions, by starting with a refactor along these lines:

static inline dma_sync_x(...)
{
	if (IS_ENABLED(CONFIG_NEED_DMA_SYNC))
		__dma_sync_x(...);
}

Cheers,
Robin.
Simon Horman Jan. 31, 2024, 4:52 p.m. UTC | #4 
On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
> Some platforms do have DMA, but DMA there is always direct and coherent.
> Currently, even on such platforms DMA sync operations are compiled and
> called.
> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
> either sync operations are needed or there is DMA ops or swiotlb
> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
> depending on this symbol state and don't call sync ops when
> dma_skip_sync() is true.
> The change allows for future optimizations of DMA sync calls depending
> on compile-time or runtime conditions.
> 
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>

Hi Alexander,

This seems to cause x86_64 allmodconfig builds to fail:

 ../drivers/media/platform/ti/omap3isp/ispstat.c:82:35: error: ‘dma_sync_single_range_for_device’ undeclared (first use in this function); did you mean ‘dma_sync_sgtable_for_device’?
    82 |                                   dma_sync_single_range_for_device);
       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       |                                   dma_sync_sgtable_for_device
 ../drivers/media/platform/ti/omap3isp/ispstat.c:82:35: note: each undeclared identifier is reported only once for each function it appears in
 ../drivers/media/platform/ti/omap3isp/ispstat.c: In function ‘isp_stat_buf_sync_magic_for_cpu’:
 ../drivers/media/platform/ti/omap3isp/ispstat.c:94:35: error: ‘dma_sync_single_range_for_cpu’ undeclared (first use in this function); did you mean ‘dma_sync_sgtable_for_cpu’?
    94 |                                   dma_sync_single_range_for_cpu);
       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       |                                   dma_sync_sgtable_for_cpu
Robin Murphy Jan. 31, 2024, 5:14 p.m. UTC | #5 
On 31/01/2024 4:52 pm, Simon Horman wrote:
> On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
>> Some platforms do have DMA, but DMA there is always direct and coherent.
>> Currently, even on such platforms DMA sync operations are compiled and
>> called.
>> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
>> either sync operations are needed or there is DMA ops or swiotlb
>> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
>> depending on this symbol state and don't call sync ops when
>> dma_skip_sync() is true.
>> The change allows for future optimizations of DMA sync calls depending
>> on compile-time or runtime conditions.
>>
>> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> 
> Hi Alexander,
> 
> This seems to cause x86_64 allmodconfig builds to fail:

Oh yeah, the sync_single_range definitions shouldn't need touching at 
all, since they're unconditional wrappers around regular sync_single 
invocations (which already may or may not do anything).

Thanks,
Robin.

> 
>   ../drivers/media/platform/ti/omap3isp/ispstat.c:82:35: error: ‘dma_sync_single_range_for_device’ undeclared (first use in this function); did you mean ‘dma_sync_sgtable_for_device’?
>      82 |                                   dma_sync_single_range_for_device);
>         |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         |                                   dma_sync_sgtable_for_device
>   ../drivers/media/platform/ti/omap3isp/ispstat.c:82:35: note: each undeclared identifier is reported only once for each function it appears in
>   ../drivers/media/platform/ti/omap3isp/ispstat.c: In function ‘isp_stat_buf_sync_magic_for_cpu’:
>   ../drivers/media/platform/ti/omap3isp/ispstat.c:94:35: error: ‘dma_sync_single_range_for_cpu’ undeclared (first use in this function); did you mean ‘dma_sync_sgtable_for_cpu’?
>      94 |                                   dma_sync_single_range_for_cpu);
>         |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         |                                   dma_sync_sgtable_for_cpu
diff mbox series

Patch

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index d62f5957f36b..1c9ff05b1ecb 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -107,6 +107,10 @@  config DMA_BOUNCE_UNALIGNED_KMALLOC
 	bool
 	depends on SWIOTLB
 
+config DMA_NEED_SYNC
+	def_bool ARCH_HAS_SYNC_DMA_FOR_DEVICE || ARCH_HAS_SYNC_DMA_FOR_CPU || \
+		 ARCH_HAS_SYNC_DMA_FOR_CPU_ALL || DMA_OPS || SWIOTLB
+
 config DMA_RESTRICTED_POOL
 	bool "DMA Restricted Pool"
 	depends on OF && OF_RESERVED_MEM && SWIOTLB
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4a658de44ee9..9dd7e1578bf6 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -117,14 +117,14 @@  dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs);
 void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
 		enum dma_data_direction dir, unsigned long attrs);
-void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
-		enum dma_data_direction dir);
-void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
-		size_t size, enum dma_data_direction dir);
-void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
-		    int nelems, enum dma_data_direction dir);
-void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
-		       int nelems, enum dma_data_direction dir);
+void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
+			       size_t size, enum dma_data_direction dir);
+void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
+				  size_t size, enum dma_data_direction dir);
+void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
+			   int nelems, enum dma_data_direction dir);
+void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
+			      int nelems, enum dma_data_direction dir);
 void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 		gfp_t flag, unsigned long attrs);
 void dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
@@ -147,7 +147,6 @@  u64 dma_get_required_mask(struct device *dev);
 bool dma_addressing_limited(struct device *dev);
 size_t dma_max_mapping_size(struct device *dev);
 size_t dma_opt_mapping_size(struct device *dev);
-bool dma_need_sync(struct device *dev, dma_addr_t dma_addr);
 unsigned long dma_get_merge_boundary(struct device *dev);
 struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
 		enum dma_data_direction dir, gfp_t gfp, unsigned long attrs);
@@ -195,20 +194,24 @@  static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs)
 {
 }
-static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
-		size_t size, enum dma_data_direction dir)
+static inline void __dma_sync_single_for_cpu(struct device *dev,
+					     dma_addr_t addr, size_t size,
+					     enum dma_data_direction dir)
 {
 }
-static inline void dma_sync_single_for_device(struct device *dev,
-		dma_addr_t addr, size_t size, enum dma_data_direction dir)
+static inline void __dma_sync_single_for_device(struct device *dev,
+						dma_addr_t addr, size_t size,
+						enum dma_data_direction dir)
 {
 }
-static inline void dma_sync_sg_for_cpu(struct device *dev,
-		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
+static inline void __dma_sync_sg_for_cpu(struct device *dev,
+					 struct scatterlist *sg, int nelems,
+					 enum dma_data_direction dir)
 {
 }
-static inline void dma_sync_sg_for_device(struct device *dev,
-		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
+static inline void __dma_sync_sg_for_device(struct device *dev,
+					    struct scatterlist *sg, int nelems,
+					    enum dma_data_direction dir)
 {
 }
 static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
@@ -277,10 +280,6 @@  static inline size_t dma_opt_mapping_size(struct device *dev)
 {
 	return 0;
 }
-static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
-{
-	return false;
-}
 static inline unsigned long dma_get_merge_boundary(struct device *dev)
 {
 	return 0;
@@ -348,20 +347,55 @@  static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
 	return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
 }
 
-static inline void dma_sync_single_range_for_cpu(struct device *dev,
-		dma_addr_t addr, unsigned long offset, size_t size,
-		enum dma_data_direction dir)
+static inline void
+__dma_sync_single_range_for_cpu(struct device *dev, dma_addr_t addr,
+				unsigned long offset, size_t size,
+				enum dma_data_direction dir)
 {
-	return dma_sync_single_for_cpu(dev, addr + offset, size, dir);
+	__dma_sync_single_for_cpu(dev, addr + offset, size, dir);
 }
 
-static inline void dma_sync_single_range_for_device(struct device *dev,
-		dma_addr_t addr, unsigned long offset, size_t size,
-		enum dma_data_direction dir)
+static inline void
+__dma_sync_single_range_for_device(struct device *dev, dma_addr_t addr,
+				   unsigned long offset, size_t size,
+				   enum dma_data_direction dir)
 {
-	return dma_sync_single_for_device(dev, addr + offset, size, dir);
+	__dma_sync_single_for_device(dev, addr + offset, size, dir);
 }
 
+#ifdef CONFIG_DMA_NEED_SYNC
+
+#define dma_skip_sync(dev)			false
+
+bool dma_need_sync(struct device *dev, dma_addr_t dma_addr);
+
+#else /* !CONFIG_DMA_NEED_SYNC */
+
+#define dma_skip_sync(dev)			true
+#define dma_need_sync(dev, dma_addr)		false
+
+#endif /* !CONFIG_DMA_NEED_SYNC */
+
+#define dma_check_sync(op, dev, ...)					  \
+	do {								  \
+		if (!dma_skip_sync(dev))				  \
+			op(dev, __VA_ARGS__);				  \
+	} while (0)
+
+#define dma_sync_single_for_cpu(d, a, s, r)				  \
+	dma_check_sync(__dma_sync_single_for_cpu, d, a, s, r)
+#define dma_sync_single_for_device(d, a, s, r)				  \
+	dma_check_sync(__dma_sync_single_for_device, d, a, s, r)
+#define dma_sync_sg_for_cpu(d, s, n, r)					  \
+	dma_check_sync(__dma_sync_sg_for_cpu, d, s, n, r)
+#define dma_sync_sg_for_device(d, s, n, r)				  \
+	dma_check_sync(__dma_sync_sg_for_device, d, s, n, r)
+
+#define dma_sync_single_range_for_cpu(d, a, o, s, r)			  \
+	dma_check_sync(__dma_sync_single_range_for_cpu, d, a, o, s, r)
+#define dma_sync_single_range_for_device(d, a, o, s, r)			  \
+	dma_check_sync(__dma_sync_single_range_for_device, d, a, o, s, r)
+
 /**
  * dma_unmap_sgtable - Unmap the given buffer for DMA
  * @dev:	The device for which to perform the DMA operation
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 58db8fd70471..a30f37f9d4db 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -329,8 +329,8 @@  void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
 }
 EXPORT_SYMBOL(dma_unmap_resource);
 
-void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
-		enum dma_data_direction dir)
+void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
+			       size_t size, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
@@ -341,10 +341,10 @@  void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
 		ops->sync_single_for_cpu(dev, addr, size, dir);
 	debug_dma_sync_single_for_cpu(dev, addr, size, dir);
 }
-EXPORT_SYMBOL(dma_sync_single_for_cpu);
+EXPORT_SYMBOL(__dma_sync_single_for_cpu);
 
-void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
-		size_t size, enum dma_data_direction dir)
+void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
+				  size_t size, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
@@ -355,10 +355,10 @@  void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
 		ops->sync_single_for_device(dev, addr, size, dir);
 	debug_dma_sync_single_for_device(dev, addr, size, dir);
 }
-EXPORT_SYMBOL(dma_sync_single_for_device);
+EXPORT_SYMBOL(__dma_sync_single_for_device);
 
-void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
-		    int nelems, enum dma_data_direction dir)
+void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
+			   int nelems, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
@@ -369,10 +369,10 @@  void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
 		ops->sync_sg_for_cpu(dev, sg, nelems, dir);
 	debug_dma_sync_sg_for_cpu(dev, sg, nelems, dir);
 }
-EXPORT_SYMBOL(dma_sync_sg_for_cpu);
+EXPORT_SYMBOL(__dma_sync_sg_for_cpu);
 
-void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
-		       int nelems, enum dma_data_direction dir)
+void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
+			      int nelems, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
@@ -383,7 +383,7 @@  void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 		ops->sync_sg_for_device(dev, sg, nelems, dir);
 	debug_dma_sync_sg_for_device(dev, sg, nelems, dir);
 }
-EXPORT_SYMBOL(dma_sync_sg_for_device);
+EXPORT_SYMBOL(__dma_sync_sg_for_device);
 
 /*
  * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems
@@ -841,6 +841,7 @@  size_t dma_opt_mapping_size(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(dma_opt_mapping_size);
 
+#ifdef CONFIG_DMA_NEED_SYNC
 bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -850,6 +851,7 @@  bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 	return ops->sync_single_for_cpu || ops->sync_single_for_device;
 }
 EXPORT_SYMBOL_GPL(dma_need_sync);
+#endif /* CONFIG_DMA_NEED_SYNC */
 
 unsigned long dma_get_merge_boundary(struct device *dev)
 {