Bug 207473

Summary: pipe performance regression on arm64
Product: File System Reporter: huhai (huhai)
Component: VFSAssignee: fs_vfs
Status: NEW ---    
Severity: normal CC: huhai, regressions, sam
Priority: P1    
Hardware: ARM   
OS: Linux   
Kernel Version: 5.7-rc3 Subsystem:
Regression: No Bisected commit-id:

Description huhai 2020-04-28 08:30:12 UTC 
Machine: FT2000+/64 (64 core with 8 numa node) or Kunpeng 920(128 core with 4 numa node)

Hi,

When I run the latest kernel(5.7-rc3) on my machine,
I use make -j64 or make -j128 to compile the kernel.

When make runs for about 10 seconds, it becomes very slow,
and like using a single thread to compile the kernel(I use
htop to observe, only one core is running).

After this, I use "git bisect" to find which patch caused
this phenomenon, I find when 6718b6f855 ("pipe: Allow
pipes to have kernel-reserved slots" and a series of pipe
related patches are added, the problem is repeated.

Thanks,
huhai