On 2020/7/9 17:10, Zhenyu Ye wrote: > + /* > + * When cpu does not support TLBI RANGE feature, we flush the tlb > + * entries one by one at the granularity of 'stride'. > + * When cpu supports the TLBI RANGE feature, then: > + * 1. If pages is odd, flush the first page through non-RANGE > + * instruction; > + * 2. For remaining pages: The minimum range granularity is decided > + * by 'scale', so we can not flush all pages by one instruction > + * in some cases. > + * > + * For example, when the pages = 0xe81a, let's start 'scale' from > + * maximum, and find right 'num' for each 'scale': > + * > + * When scale = 3, we can flush no pages because the minumum > + * range is 2^(5*3 + 1) = 0x10000. > + * When scale = 2, the minimum range is 2^(5*2 + 1) = 0x800, we can > + * flush 0xe800 pages this time, the num = 0xe800/0x800 - 1 = 0x1c. > + * Remain pages is 0x1a; > + * When scale = 1, the minimum range is 2^(5*1 + 1) = 0x40, no page > + * can be flushed. > + * When scale = 0, we flush the remaining 0x1a pages, the num = > + * 0x1a/0x2 - 1 = 0xd. > + * > + * However, in most scenarios, the pages = 1 when flush_tlb_range() is > + * called. Start from scale = 3 or other proper value (such as scale = > + * ilog2(pages)), will incur extra overhead. > + * So increase 'scale' from 0 to maximum, the flush order is exactly > + * opposite to the example. > + */ The comments may be too long, probably should be moved to commit messages. Thanks, Zhenyu
