Re: [REGRESSION]: mmap performance regression starting with k-6.1

[Bagas Sanjaya]

On Wed, Nov 22, 2023 at 08:03:19PM +0000, Chun Ng wrote:
> Hi,
> 
> Recently I observed there is performance regression on system call mmap(..). I tried both vanilla kernels and Raspberry Pi kernels on a Raspberry Pi 4 box and the results are pretty consistent among them.
> 
> Bisection showed that the regression starts from k-6.1, and the latest vanilla k-6.7 is still showing the same regression.
> 
> The test program calls mmap/munmap for a 4K page with MAP_ANON and MAP_PRIVATE flags, and ftrace is used to measure the time spent on the do_mmap(..) call.  Measured time of a sample run with different vanilla kernel versions are:
> k-5.10 and k-6.0: ~157us
> k-6.1: ~194us
> k-6.7: ~214us
> Results are pretty consistent across multiple runs with a small percentage variance.  Ftrace shows that latency of mmap_region(...) has increased since k-6.1.  An application that makes frequent mmap(..) calls the accumulated extra latency is very noticeable. 
> 
> Please find the ftrace results and kernel config files in this folder:
> https://drive.google.com/drive/folders/1qy8YTBqxu8Gdbs7IigYbSd4FXldId5sd?usp=drive_link
> 
> The test program can be found in here:
> https://drive.google.com/file/d/1tG6_BbQMCHwfKebvAIAg_xqbM_lpPcuM/view?usp=sharing
> 
> Info on the testing environment:
> cpufreq_governor: performance
> Test machine: Raspberry Pi 4, 8GB DDR
> SCHED_FIFO with priority 99 for running the test program
> 
> Vanilla kernels are not tainted. However on k-6.0 and k-6.7, I have to patch the drivers/clk/bcm/clk-raspberrypi.c file with the version in Raspberry Pi kernel tree for the CPU frequency governor to work.
> 

The next step is to find the commit that introduces your regression with
`git bisect`. If you haven't done so, see
Documentation/admin-guide/bug-bisect.rst for instructions.

Anyway, I'm adding this regression to regzbot:

#regzbot ^introduced: v6.0..v6.1

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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