Re: [RFC PATCH v2] arm64: cpufeatures: add support for tlbi range instructions

Will Deacon
2019-11-11T13:27:24Z

On Mon, Nov 11, 2019 at 09:23:55PM +0800, Zhenyu Ye wrote:
> ARMv8.4-TLBI provides TLBI invalidation instruction that apply to a
> range of input addresses. This patch adds support for this feature.
> This is the second version of the patch.
>
> I traced the __flush_tlb_range() for a minute and get some statistical
> data as below:
>
> PAGENUM COUNT
> 1 34944
> 2 5683
> 3 1343
> 4 7857
> 5 838
> 9 339
> 16 933
> 19 427
> 20 5821
> 23 279
> 41 338
> 141 279
> 512 428
> 1668 120
> 2038 100
>
> Those data are based on kernel-5.4.0, where PAGENUM = end - start, COUNT
> shows number of calls to the __flush_tlb_range() in a minute. There only
> shows the data which COUNT >= 100. The kernel is started normally, and
> transparent hugepage is opened. As we can see, though most user TLBI
> ranges were 1 pages long, the num of long-range can not be ignored.
>
> The new feature of TLB range can improve lots of performance compared to
> the current implementation. As an example, flush 512 ranges needs only 1
> instruction as opposed to 512 instructions using current implementation.
>
> And for a new hardware feature, support is better than not.
>
> Signed-off-by: Zhenyu Ye <yezhenyu2@huawei.com>
> ---
> ChangeLog v1 -> v2:
> - Change the main implementation of this feature.
> - Add some comments.

How does this address my concerns here:

https://lore.kernel.org/linux-arm-kernel/20191031131649.GB27196@willie-the-truck/

?

Will