Re: [linux-next:master] [btrfs] 8d99361835: stress-ng.link.ops_per_sec -18.0% regression

[Qu Wenruo <wqu@suse.com>]

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On 2024/1/3 02:56, David Sterba wrote:
> On Fri, Dec 22, 2023 at 05:59:34PM +0800, kernel test robot wrote:
>>
>>
>> Hello,
>>
>> kernel test robot noticed a -18.0% regression of stress-ng.link.ops_per_sec on:
>>
>>
>> commit: 8d993618350c86da11cb408ba529c13e83d09527 ("btrfs: migrate get_eb_page_index() and get_eb_offset_in_page() to folios")
>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> 
> Unfortunatelly the conversion to folios adds a lot of assembly code and
> we can't rely on constants like PAGE_SIZE anymore. The calculations in
> extent buffer members are therefore slower, 18% is a lot but within my
> expected range for metadta-only operations.
> 
> This could be improved by caching some values, like folio_size, so it's
> a dereference and not a calculation of "PAGE_SIZE << folio_order" with
> conditionals around.

Yep, caching the folio size is also on my todo list.

I'm pretty happy to add that, but it may still be slower than handling a 
fixed PAGE_SIZE, I'm not sure how much it would improve.

Thanks,
Qu

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