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Message-ID: <20180416122706.GA20624@infradead.org>
Date: Mon, 16 Apr 2018 05:27:06 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Jesper Dangaard Brouer <brouer@...hat.com>
Cc: "xdp-newbies@...r.kernel.org" <xdp-newbies@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Christoph Hellwig <hch@....de>,
David Woodhouse <dwmw2@...radead.org>,
William Tu <u9012063@...il.com>,
Björn Töpel <bjorn.topel@...el.com>,
"Karlsson, Magnus" <magnus.karlsson@...el.com>,
Alexander Duyck <alexander.duyck@...il.com>,
Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: XDP performance regression due to CONFIG_RETPOLINE Spectre V2
Can you try the following hack which avoids indirect calls entirely
for the fast path direct mapping case?
---
>From b256a008c1b305e6a1c2afe7c004c54ad2e96d4b Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@....de>
Date: Mon, 16 Apr 2018 14:18:14 +0200
Subject: dma-mapping: bypass dma_ops for direct mappings
Reportedly the retpoline mitigation for spectre causes huge penalties
for indirect function calls. This hack bypasses the dma_ops mechanism
for simple direct mappings.
Signed-off-by: Christoph Hellwig <hch@....de>
---
include/linux/device.h | 1 +
include/linux/dma-mapping.h | 53 +++++++++++++++++++++++++++----------
lib/dma-direct.c | 4 +--
3 files changed, 42 insertions(+), 16 deletions(-)
diff --git a/include/linux/device.h b/include/linux/device.h
index 0059b99e1f25..725eec4c6653 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -990,6 +990,7 @@ struct device {
bool offline_disabled:1;
bool offline:1;
bool of_node_reused:1;
+ bool is_dma_direct:1;
};
static inline struct device *kobj_to_dev(struct kobject *kobj)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index f8ab1c0f589e..c5d384ae25d6 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -223,6 +223,13 @@ static inline const struct dma_map_ops *get_dma_ops(struct device *dev)
}
#endif
+/* do not use directly! */
+dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
+ unsigned long offset, size_t size, enum dma_data_direction dir,
+ unsigned long attrs);
+int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl,
+ int nents, enum dma_data_direction dir, unsigned long attrs);
+
static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
size_t size,
enum dma_data_direction dir,
@@ -232,9 +239,13 @@ static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
dma_addr_t addr;
BUG_ON(!valid_dma_direction(dir));
- addr = ops->map_page(dev, virt_to_page(ptr),
- offset_in_page(ptr), size,
- dir, attrs);
+ if (dev->is_dma_direct) {
+ addr = dma_direct_map_page(dev, virt_to_page(ptr),
+ offset_in_page(ptr), size, dir, attrs);
+ } else {
+ addr = ops->map_page(dev, virt_to_page(ptr),
+ offset_in_page(ptr), size, dir, attrs);
+ }
debug_dma_map_page(dev, virt_to_page(ptr),
offset_in_page(ptr), size,
dir, addr, true);
@@ -249,7 +260,7 @@ static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->unmap_page)
+ if (!dev->is_dma_direct && ops->unmap_page)
ops->unmap_page(dev, addr, size, dir, attrs);
debug_dma_unmap_page(dev, addr, size, dir, true);
}
@@ -266,7 +277,10 @@ static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
int ents;
BUG_ON(!valid_dma_direction(dir));
- ents = ops->map_sg(dev, sg, nents, dir, attrs);
+ if (dev->is_dma_direct)
+ ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
+ else
+ ents = ops->map_sg(dev, sg, nents, dir, attrs);
BUG_ON(ents < 0);
debug_dma_map_sg(dev, sg, nents, ents, dir);
@@ -281,7 +295,7 @@ static inline void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg
BUG_ON(!valid_dma_direction(dir));
debug_dma_unmap_sg(dev, sg, nents, dir);
- if (ops->unmap_sg)
+ if (!dev->is_dma_direct && ops->unmap_sg)
ops->unmap_sg(dev, sg, nents, dir, attrs);
}
@@ -295,7 +309,10 @@ static inline dma_addr_t dma_map_page_attrs(struct device *dev,
dma_addr_t addr;
BUG_ON(!valid_dma_direction(dir));
- addr = ops->map_page(dev, page, offset, size, dir, attrs);
+ if (dev->is_dma_direct)
+ addr = dma_direct_map_page(dev, page, offset, size, dir, attrs);
+ else
+ addr = ops->map_page(dev, page, offset, size, dir, attrs);
debug_dma_map_page(dev, page, offset, size, dir, addr, false);
return addr;
@@ -309,7 +326,7 @@ static inline void dma_unmap_page_attrs(struct device *dev,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->unmap_page)
+ if (!dev->is_dma_direct && ops->unmap_page)
ops->unmap_page(dev, addr, size, dir, attrs);
debug_dma_unmap_page(dev, addr, size, dir, false);
}
@@ -356,7 +373,7 @@ static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->sync_single_for_cpu)
+ if (!dev->is_dma_direct && ops->sync_single_for_cpu)
ops->sync_single_for_cpu(dev, addr, size, dir);
debug_dma_sync_single_for_cpu(dev, addr, size, dir);
}
@@ -368,7 +385,7 @@ static inline void dma_sync_single_for_device(struct device *dev,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->sync_single_for_device)
+ if (!dev->is_dma_direct && ops->sync_single_for_device)
ops->sync_single_for_device(dev, addr, size, dir);
debug_dma_sync_single_for_device(dev, addr, size, dir);
}
@@ -382,7 +399,7 @@ static inline void dma_sync_single_range_for_cpu(struct device *dev,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->sync_single_for_cpu)
+ if (!dev->is_dma_direct && ops->sync_single_for_cpu)
ops->sync_single_for_cpu(dev, addr + offset, size, dir);
debug_dma_sync_single_range_for_cpu(dev, addr, offset, size, dir);
}
@@ -396,7 +413,7 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->sync_single_for_device)
+ if (!dev->is_dma_direct && ops->sync_single_for_device)
ops->sync_single_for_device(dev, addr + offset, size, dir);
debug_dma_sync_single_range_for_device(dev, addr, offset, size, dir);
}
@@ -408,7 +425,7 @@ dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->sync_sg_for_cpu)
+ if (!dev->is_dma_direct && ops->sync_sg_for_cpu)
ops->sync_sg_for_cpu(dev, sg, nelems, dir);
debug_dma_sync_sg_for_cpu(dev, sg, nelems, dir);
}
@@ -420,7 +437,7 @@ dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
const struct dma_map_ops *ops = get_dma_ops(dev);
BUG_ON(!valid_dma_direction(dir));
- if (ops->sync_sg_for_device)
+ if (!dev->is_dma_direct && ops->sync_sg_for_device)
ops->sync_sg_for_device(dev, sg, nelems, dir);
debug_dma_sync_sg_for_device(dev, sg, nelems, dir);
@@ -600,6 +617,8 @@ static inline int dma_supported(struct device *dev, u64 mask)
return ops->dma_supported(dev, mask);
}
+extern const struct dma_map_ops swiotlb_dma_ops;
+
#ifndef HAVE_ARCH_DMA_SET_MASK
static inline int dma_set_mask(struct device *dev, u64 mask)
{
@@ -609,6 +628,12 @@ static inline int dma_set_mask(struct device *dev, u64 mask)
dma_check_mask(dev, mask);
*dev->dma_mask = mask;
+ if (dev->dma_ops == &dma_direct_ops ||
+ (dev->dma_ops == &swiotlb_dma_ops &&
+ mask == DMA_BIT_MASK(64)))
+ dev->is_dma_direct = true;
+ else
+ dev->is_dma_direct = false;
return 0;
}
#endif
diff --git a/lib/dma-direct.c b/lib/dma-direct.c
index c0bba30fef0a..3deb8666974b 100644
--- a/lib/dma-direct.c
+++ b/lib/dma-direct.c
@@ -120,7 +120,7 @@ void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
free_pages((unsigned long)cpu_addr, page_order);
}
-static dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
+dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
unsigned long offset, size_t size, enum dma_data_direction dir,
unsigned long attrs)
{
@@ -131,7 +131,7 @@ static dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
return dma_addr;
}
-static int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl,
+int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl,
int nents, enum dma_data_direction dir, unsigned long attrs)
{
int i;
--
2.17.0
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