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


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