c++ NEON Copy但非memcpy最终导致ARM Linux内存碎片

kmpatx3s  于 2022-12-01  发布在  Linux
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我在BeagleBone X-15(ARM Cortex-A15)板上运行Linux 4.4。我的应用程序mmap SGX GPU的输出,需要复制DRM后备存储。
memcpy和我的自定义NEON复制代码都可以工作...但是NEON代码要快得多(~ 11 ms vs. ~ 35 ms)。
我注意到,在12500秒之后,当我使用NEON版本的副本时,Linux会因为内存不足(OOM)而终止应用程序。当我运行应用程序并将一行从NEON副本更改为标准memcpy时,它会无限期地运行(到目前为止运行了12个小时......)。但复制速度较慢。
我已经粘贴了mmap、copy和NEON copy的代码。我的NEON copy真的有什么问题吗?
NEON文案:

/**
* CompOpenGL neonCopyRGBAtoRGBA()
* Purpose: neonCopyRGBAtoRGBA - Software NEON copy
*
* @param src - Source buffer
* @param dst - Destination buffer
* @param numpix - Number of pixels to convert
*/
__attribute__((noinline)) void CompOpenGL::neonCopyRGBAtoRGBA(unsigned char* src, unsigned char* dst, int numPix)
{

    (void)src;
    (void)dst;
    (void)numPix;

    // This case takes RGBA -> BGRA
    __asm__ volatile(
                "mov r3, r3, lsr #3\n"           /* Divide number of pixels by 8 because we process them 8 at a time */
                "loopRGBACopy:\n"
                "vld4.8 {d0-d3}, [r1]!\n"        /* Load 8 pixels into d0 through d2. d0 = R[0-7], d1 = G[0-7], d2 = B[0-7], d3 = A[0-7] */
                "subs r3, r3, #1\n"              /* Decrement the loop counter */
                "vst4.8 {d0-d3}, [r2]!\n"        /* Store the RGBA into destination 8 pixels at a time */
                "bgt loopRGBACopy\n"
                "bx lr\n"
                );

}

Mmap并将代码复制到此处:

union gbm_bo_handle handleUnion = gbm_bo_get_handle(m_Fb->bo);
struct drm_omap_gem_info gemInfo;
char *gpuMmapFrame = NULL;
gemInfo.handle = handleUnion.s32;
int ret = drmCommandWriteRead(m_DRMController->m_Fd, DRM_OMAP_GEM_INFO,&gemInfo, sizeof(gemInfo));
if (ret) {
    qDebug() << "Cannot set write/read";
}
else {
    // Mmap the frame
    gpuMmapFrame = (char *)mmap(0, gemInfo.size, PROT_READ | PROT_WRITE, MAP_SHARED,m_DRMController->m_Fd, gemInfo.offset);

    if ( gpuMmapFrame != MAP_FAILED ) {

        QElapsedTimer timer;
        timer.restart();
        
        //m_OGLController->neonCopyRGBAtoRGBA((uchar*)gpuMmapFrame,  (uchar*)m_cpyFrame,dmaBuf.width * dmaBuf.height);
        memcpy(m_cpyFrame,gpuMmapFrame,dmaBuf.height * dmaBuf.width * 4);
        
        qDebug() << "Copy Performance: " << timer.elapsed();
7cwmlq89

7cwmlq891#

好消息是,如果将vld4/vst4替换为vld1/vst1,函数的运行速度会快很多。
坏消息是,您必须报告您使用和修改了哪些寄存器,包括CPSR和内存,并且您不应该从内联汇编(bx lr)返回。

__asm__ volatile(
                "mov r3, r3, lsr #3\n"           /* Divide number of pixels by 8 because we process them 8 at a time */
                "loopRGBACopy:\n"
                "vld1.8 {d0-d3}, [r1]!\n"        /* Load 8 pixels into d0 through d2. d0 = R[0-7], d1 = G[0-7], d2 = B[0-7], d3 = A[0-7] */
                "subs r3, r3, #1\n"              /* Decrement the loop counter */
                "vst1.8 {d0-d3}, [r2]!\n"        /* Store the RGBA into destination 8 pixels at a time */
                "bgt loopRGBACopy\n"
                ::: "r1", "r2", "r3", "d0", "d1", "d2", "d3", "cc", "memory"
                );

http://www.ethernut.de/en/documents/arm-inline-asm.html

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