prefetch

问题 I\'m writing a program to analyze a graph of social network. It means the program needs a lot of random memory accesses. It seems to me prefetch should help. Here is a small piece of the code of reading values from neighbors of a vertex. for (size_t i = 0; i < v.get_num_edges(); i++) { unsigned int id = v.neighbors[i]; res += neigh_vals[id]; } I transform the code above to the one as below and prefetch the values of the neighbors of a vertex. int *neigh_vals = new int[num_vertices]; for (size

问题 suppose I have this model: class PhotoAlbum(models.Model): title = models.CharField(max_length=128) author = models.CharField(max_length=128) class Photo(models.Model): album = models.ForeignKey(\'PhotoAlbum\') format = models.IntegerField() Now if I want to look at a subset of photos in a subset of albums efficiently. I do it something like this: someAlbums = PhotoAlbum.objects.filter(author=\"Davey Jones\").prefetch_related(\"photo_set\") for a in someAlbums: somePhotos = a.photo_set.all()

问题 Can anyone give an example or a link to an example which uses __builtin_prefetch in GCC (or just the asm instruction prefetcht0 in general) to gain a substantial performance advantage? In particular, I\'d like the example to meet the following criteria: It is a simple, small, self-contained example. Removing the __builtin_prefetch instruction results in performance degradation. Replacing the __builtin_prefetch instruction with the corresponding memory access results in performance degradation

问题 I would like to programmatically disable hardware prefetching. From Optimizing Application Performance on Intel® Core™ Microarchitecture Using Hardware-Implemented Prefetchers and How to Choose between Hardware and Software Prefetch on 32-Bit Intel® Architecture, I need to update the MSR to disable hardware prefetching. Here is a relevant snippet: \"DPL Prefetch and L2 Streaming Prefetch settings can also be changed programmatically by writing a device driver utility for changing the bits in

问题 When executing a series of _mm_stream_load_si128() calls ( MOVNTDQA ) from consecutive memory locations, will the hardware pre-fetcher still kick-in, or should I use explicit software prefetching (with NTA hint) in order to obtain the benefits of prefetching while still avoiding cache pollution? The reason I ask this is because their objectives seem contradictory to me. A streaming load will fetch data bypassing the cache, while the pre-fetcher attempts to proactively fetch data into the