On Mon, 15 Jun 2020 at 09:42, Manuel Wolfshant <wolfy@xxxxxxxxxxxxxxxxxx> wrote:
On 6/15/20 2:46 PM, Stephen John Smoogen wrote:
I got inspired by Adi's earlier suggestion and after reading https://access.redhat.com/articles/3311301 I've tried today all variants of disabling the spectre mitigations. Whatever I do, immediately after a reboot, yum reinstall kernel does not take less than 5 minutes :( It goes down to 2 min if I repeat the operation afterwards so I guess some caching kicks in. I will try later today the kernels from elrepo and maybe even xen.crc.id.au ( I kind of hate the "disable selinux" recommendation from the install page so I postponed it in the hope of other solution ).
If you can do a full reinstall, could you see if a KVM host/guest combo has the same problem? That would at least point the finger more firmly at VT, spectre or something else.
I finally managed to install a fresh KVM host / guest pair on an identical blade ( HS21XM, 64 GB ram, 2*E5450@ 3.00GHz ). Here are the results I see:
#cd /sys/kernel/debug/x86/
#cat ibrs_enabled pti_enabled retp_enabled
0
1
1
#time yum -y reinstall kernel-3.10.0-1127.el7.x86_64
real 0m50.026s
user 0m32.872s
sys 0m23.312s
2. KVM guest on the same machine (virt-install --name guest1-rhel7 --memory 2048 --vcpus 2 --disk size=20 --network=bridge:br0 --pxe --os-variant rhel7 <=== copy/paste from https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-guest_virtual_machine_installation_overview-creating_guests_with_virt_install ), stock installation and fully updated with absolutely no change towards the defaults including same ibrs_enabled pti_enabled retp_enabled as the host, , kernel 3.10.0-1127.10.1
#time yum -y reinstall kernel-3.10.0-1127.el7.x86_64
real 2m39.644s
user 1m54.662s
sys 1m32.496s
3. Xen Domu, 3.10.0-1127.8.2.el7.x86_6 ( but results are
consistent across all kernels )
# cat ibrs_enabled pti_enabled retp_enabled
0
0
0
# time yum -y reinstall kernel-3.10.0-1127.el7.x86_64
real 5m44.030s
user 2m9.931s
sys 4m7.771s
4. Dom0, 4.9.215-36.el7.x86_64, , xen 4.12 from centos' repo
# time yum -y reinstall kernel-3.10.0-1127.el7.x86_64
real 1m52.417s
user 0m45.704s
sys 1m32.167s
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