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linuxaffinityhotplugging
Xenen GLiu
Xenen GLiu

Reputation: 19

Linux cpu hotplug not working as expected

I'm testing linux cpu hotpluging on normal 4-core ARM based on Android 8.1 kernel 4.4 sys. Problem seems that after onlining a CPU again taskset and kernel refuses to move and/or schedule any tasks on the core. E.g. doing:

echo 0 > /sys/devices/system/cpu/cpu3/online
echo 1 > /sys/devices/system/cpu/cpu3/online
taskset -c 3 bash

Fails... I don't know why taskset refuses to migrate any threads to the hotpluged cores. I have intend to use this to improve the kernel NO_HZ tickless operation by forcing Local timer interupts (LOC) off from cores 1-3. The kernel NO_HZ documentation suggests this possibility.

I also run it on upstream kernerl 4.18.4 on Linux qemu. it is also exist. please give me some help,thanks~

Upvotes: 1

Views: 253

Answers (1)

Mohammad moein Aghtaei
Mohammad moein Aghtaei

Reputation: 47

Use this for hotplug and add CPU and RAM without rebooting.

#!/bin/bash

# Bring CPUs online
for CPU_DIR in /sys/devices/system/cpu/cpu[0-9]*
do
    CPU=${CPU_DIR##*/}
    echo "Found cpu: '${CPU_DIR}' ..."
    CPU_STATE_FILE="${CPU_DIR}/online"
    if [ -f "${CPU_STATE_FILE}" ]; then
        if grep -qx 1 "${CPU_STATE_FILE}"; then
            echo -e "\t${CPU} already online"
        else
            echo -e "\t${CPU} is new cpu, onlining cpu ..."
            echo 1 > "${CPU_STATE_FILE}"
        fi
    else 
        echo -e "\t${CPU} already configured prior to hot-add"
    fi
done

# Bring all new Memory online
for RAM in $(grep line /sys/devices/system/memory/*/state)
do
    echo "Found ram: ${RAM} ..."
    if [[ "${RAM}" == *":offline" ]]; then
        echo "Bringing online"
        echo $RAM | sed "s/:offline$//"|sed "s/^/echo online > /"|source /dev/stdin
    else
        echo "Already online"
    fi
done

Upvotes: 0

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