drm: Add a prefetching memcpy_from_wc

Reading out of write-combining mapped memory is typically very slow
since the CPU doesn't prefetch. However some archs have special
instructions to do this.

So add a best-effort memcpy_from_wc taking dma-buf-map pointer
arguments that attempts to use a fast prefetching memcpy and
otherwise falls back to ordinary memcopies, taking the iomem tagging
into account.

The code is largely copied from i915_memcpy_from_wc.

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Christian König <christian.koenig@amd.com>
Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://lore.kernel.org/r/20210602083818.241793-5-thomas.hellstrom@linux.intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20210602083818.241793-5-thomas.hellstrom@linux.intel.com
This commit is contained in:
Thomas Hellström 2021-06-02 10:38:11 +02:00
parent 3bf3710e37
commit b7e32bef4a
4 changed files with 159 additions and 2 deletions

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@ -469,8 +469,8 @@ DRM MM Range Allocator Function References
.. kernel-doc:: drivers/gpu/drm/drm_mm.c
:export:
DRM Cache Handling
==================
DRM Cache Handling and Fast WC memcpy()
=======================================
.. kernel-doc:: drivers/gpu/drm/drm_cache.c
:export:

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@ -28,6 +28,7 @@
* Authors: Thomas Hellström <thomas-at-tungstengraphics-dot-com>
*/
#include <linux/dma-buf-map.h>
#include <linux/export.h>
#include <linux/highmem.h>
#include <linux/mem_encrypt.h>
@ -35,6 +36,9 @@
#include <drm/drm_cache.h>
/* A small bounce buffer that fits on the stack. */
#define MEMCPY_BOUNCE_SIZE 128
#if defined(CONFIG_X86)
#include <asm/smp.h>
@ -209,3 +213,147 @@ bool drm_need_swiotlb(int dma_bits)
return max_iomem > ((u64)1 << dma_bits);
}
EXPORT_SYMBOL(drm_need_swiotlb);
static void memcpy_fallback(struct dma_buf_map *dst,
const struct dma_buf_map *src,
unsigned long len)
{
if (!dst->is_iomem && !src->is_iomem) {
memcpy(dst->vaddr, src->vaddr, len);
} else if (!src->is_iomem) {
dma_buf_map_memcpy_to(dst, src->vaddr, len);
} else if (!dst->is_iomem) {
memcpy_fromio(dst->vaddr, src->vaddr_iomem, len);
} else {
/*
* Bounce size is not performance tuned, but using a
* bounce buffer like this is significantly faster than
* resorting to ioreadxx() + iowritexx().
*/
char bounce[MEMCPY_BOUNCE_SIZE];
void __iomem *_src = src->vaddr_iomem;
void __iomem *_dst = dst->vaddr_iomem;
while (len >= MEMCPY_BOUNCE_SIZE) {
memcpy_fromio(bounce, _src, MEMCPY_BOUNCE_SIZE);
memcpy_toio(_dst, bounce, MEMCPY_BOUNCE_SIZE);
_src += MEMCPY_BOUNCE_SIZE;
_dst += MEMCPY_BOUNCE_SIZE;
len -= MEMCPY_BOUNCE_SIZE;
}
if (len) {
memcpy_fromio(bounce, _src, MEMCPY_BOUNCE_SIZE);
memcpy_toio(_dst, bounce, MEMCPY_BOUNCE_SIZE);
}
}
}
#ifdef CONFIG_X86
static DEFINE_STATIC_KEY_FALSE(has_movntdqa);
static void __memcpy_ntdqa(void *dst, const void *src, unsigned long len)
{
kernel_fpu_begin();
while (len >= 4) {
asm("movntdqa (%0), %%xmm0\n"
"movntdqa 16(%0), %%xmm1\n"
"movntdqa 32(%0), %%xmm2\n"
"movntdqa 48(%0), %%xmm3\n"
"movaps %%xmm0, (%1)\n"
"movaps %%xmm1, 16(%1)\n"
"movaps %%xmm2, 32(%1)\n"
"movaps %%xmm3, 48(%1)\n"
:: "r" (src), "r" (dst) : "memory");
src += 64;
dst += 64;
len -= 4;
}
while (len--) {
asm("movntdqa (%0), %%xmm0\n"
"movaps %%xmm0, (%1)\n"
:: "r" (src), "r" (dst) : "memory");
src += 16;
dst += 16;
}
kernel_fpu_end();
}
/*
* __drm_memcpy_from_wc copies @len bytes from @src to @dst using
* non-temporal instructions where available. Note that all arguments
* (@src, @dst) must be aligned to 16 bytes and @len must be a multiple
* of 16.
*/
static void __drm_memcpy_from_wc(void *dst, const void *src, unsigned long len)
{
if (unlikely(((unsigned long)dst | (unsigned long)src | len) & 15))
memcpy(dst, src, len);
else if (likely(len))
__memcpy_ntdqa(dst, src, len >> 4);
}
/**
* drm_memcpy_from_wc - Perform the fastest available memcpy from a source
* that may be WC.
* @dst: The destination pointer
* @src: The source pointer
* @len: The size of the area o transfer in bytes
*
* Tries an arch optimized memcpy for prefetching reading out of a WC region,
* and if no such beast is available, falls back to a normal memcpy.
*/
void drm_memcpy_from_wc(struct dma_buf_map *dst,
const struct dma_buf_map *src,
unsigned long len)
{
if (WARN_ON(in_interrupt())) {
memcpy_fallback(dst, src, len);
return;
}
if (static_branch_likely(&has_movntdqa)) {
__drm_memcpy_from_wc(dst->is_iomem ?
(void __force *)dst->vaddr_iomem :
dst->vaddr,
src->is_iomem ?
(void const __force *)src->vaddr_iomem :
src->vaddr,
len);
return;
}
memcpy_fallback(dst, src, len);
}
EXPORT_SYMBOL(drm_memcpy_from_wc);
/*
* drm_memcpy_init_early - One time initialization of the WC memcpy code
*/
void drm_memcpy_init_early(void)
{
/*
* Some hypervisors (e.g. KVM) don't support VEX-prefix instructions
* emulation. So don't enable movntdqa in hypervisor guest.
*/
if (static_cpu_has(X86_FEATURE_XMM4_1) &&
!boot_cpu_has(X86_FEATURE_HYPERVISOR))
static_branch_enable(&has_movntdqa);
}
#else
void drm_memcpy_from_wc(struct dma_buf_map *dst,
const struct dma_buf_map *src,
unsigned long len)
{
WARN_ON(in_interrupt());
memcpy_fallback(dst, src, len);
}
EXPORT_SYMBOL(drm_memcpy_from_wc);
void drm_memcpy_init_early(void)
{
}
#endif /* CONFIG_X86 */

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@ -35,6 +35,7 @@
#include <linux/slab.h>
#include <linux/srcu.h>
#include <drm/drm_cache.h>
#include <drm/drm_client.h>
#include <drm/drm_color_mgmt.h>
#include <drm/drm_drv.h>
@ -1041,6 +1042,7 @@ static int __init drm_core_init(void)
drm_connector_ida_init();
idr_init(&drm_minors_idr);
drm_memcpy_init_early();
ret = drm_sysfs_init();
if (ret < 0) {

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@ -35,6 +35,8 @@
#include <linux/scatterlist.h>
struct dma_buf_map;
void drm_clflush_pages(struct page *pages[], unsigned long num_pages);
void drm_clflush_sg(struct sg_table *st);
void drm_clflush_virt_range(void *addr, unsigned long length);
@ -70,4 +72,9 @@ static inline bool drm_arch_can_wc_memory(void)
#endif
}
void drm_memcpy_init_early(void);
void drm_memcpy_from_wc(struct dma_buf_map *dst,
const struct dma_buf_map *src,
unsigned long len);
#endif