On 4/21/20 5:25 AM, Bernard Zhao wrote: > kmalloc_index inline function code size optimization and runtime > performance stability optimization. After optimization, the function > kmalloc_index is more stable, the size will never affecte the function`s > execution efficiency. > And follow test data shows that the performance of new optimization > exceeds the original algorithm when applying for more than 512 Bytes > (include 512B).And new optimization runtime is more stable than before. > Test platform:install vmware ubuntu 16.04, ram 2G, cpu 1, i5-8500 3.00GHz > Compiler: gcc -O2 optimization, gcc version 5.4.0. > Just test diff code part. > Follow is detailed test data: > size time/Per 100 million times > old fun new fun with optimise > 8 203777 241934 > 16 245611 409278 > 32 236384 408419 > 64 275499 447732 > 128 354909 416439 > 256 360472 406598 > 512 431072 409168 > 1024 463822 407401 > 2 * 1024 548519 407710 > 4 * 1024 623378 422326 > 8 * 1024 655932 407457 > 16 * 1024 744673 417574 > 32 * 1024 824889 415316 > 64 * 1024 854374 408577 > 128 * 1024 968079 433582 > 256 * 1024 985527 412080 > 512 * 1024 1196877 448199 > 1024 * 1024 1310315 448969 > 2 * 1024 * 1024 1367441 513117 > 4 * 1024 * 1024 1264623 415019 > 8 * 1024 * 1024 1255727 417197 > 16 * 1024 * 1024 1401431 411087 > 32 * 1024 * 1024 1440415 416616 > 64 * 1024 * 1024 1428122 417459 No, the kernel will never see these time improvements (or non-improvements for small sizes). See how kmalloc() and kmalloc_node() both call kmalloc_index() only under "if (__builtin_constant_p(size))" which means kmalloc is called with a (compile-time) constant size, so this code is only evaluated at compile time, not while kernel is running. Otherwise it really wouldn't be implemented as a stream of if's :) The cases that are not compile time constant size end up in kmalloc_slab(), so you can see how that one is implemented and what its performance is.
