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Date:   Mon, 17 Feb 2020 11:03:07 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Li Zefan <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>,
        cgroups@...r.kernel.org
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [regression] cpuset: offlined CPUs removed from affinity masks

Hi,

Adding Tejun and the cgroups mailing list in CC for this cpuset regression I
reported last month.

Thanks,

Mathieu

----- On Jan 16, 2020, at 12:41 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> Hi,
> 
> I noticed the following regression with CONFIG_CPUSET=y. Note that
> I am not using cpusets at all (only using the root cpuset I'm given
> at boot), it's just configured in. I am currently working on a 5.2.5
> kernel. I am simply combining use of taskset(1) (setting the affinity
> mask of a process) and cpu hotplug. The result is that with
> CONFIG_CPUSET=y, setting the affinity mask including an offline CPU number
> don't keep that CPU in the affinity mask, and it is never put back when the
> CPU comes back online. CONFIG_CPUSET=n behaves as expected, and puts back
> the CPU into the affinity mask reported to user-space when it comes back
> online.
> 
> 
> * With CONFIG_CPUSET=y (unexpected behavior):
> 
> # echo 0 > /sys/devices/system/cpu/cpu1/online
> 
> % taskset 0x7 ./loop &
> % taskset -p $!
> pid 1341's current affinity mask: 5
> 
> # echo 1 > /sys/devices/system/cpu/cpu1/online
> 
> taskset -p $!
> pid 1341's current affinity mask: 5
> 
> kill $!
> 
> 
> * With CONFIG_CPUSET=n (expected behavior):
> 
> (Offlining CPU, then start task)
> 
> # echo 0 > /sys/devices/system/cpu/cpu1/online
> 
> % taskset 0x7 ./loop &
> % taskset -p $!
> pid 1358's current affinity mask: 5
> 
> # echo 1 > /sys/devices/system/cpu/cpu1/online
> 
> taskset -p $!
> pid 1358's current affinity mask: 7
> 
> kill $!
> 
> 
> Test system lscpu output:
> 
> Architecture:        x86_64
> CPU op-mode(s):      32-bit, 64-bit
> Byte Order:          Little Endian
> CPU(s):              32
> On-line CPU(s) list: 0-31
> Thread(s) per core:  2
> Core(s) per socket:  8
> Socket(s):           2
> NUMA node(s):        2
> Vendor ID:           GenuineIntel
> CPU family:          6
> Model:               60
> Model name:          Intel Core Processor (Haswell, no TSX, IBRS)
> Stepping:            1
> CPU MHz:             2399.996
> BogoMIPS:            4799.99
> Hypervisor vendor:   KVM
> Virtualization type: full
> L1d cache:           32K
> L1i cache:           32K
> L2 cache:            4096K
> NUMA node0 CPU(s):   0-7,16-23
> NUMA node1 CPU(s):   8-15,24-31
> Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
> cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx rdtscp lm constant_tsc
> rep_good nopl cpuid tsc_known_freq pni pclmulqdq ssse3 fma cx16 pcid sse4_1
> sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand
> hypervisor lahf_lm abm cpuid_fault invpcid_single pti ibrs ibpb fsgsbase bmi1
> avx2 smep bmi2 erms invpcid xsaveopt
> 
> 
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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