Hello,
I have a X99 system with i7 5820K, which is used to run a emulator on X86; In the emulator the EPT is used to accelerate the address translating.
After switch to "3.10.0-693.11.6.el7.x86_64", the performance dropped 60-80% without any error from the EPT kernel module; If switch back to old kernel everything is back normal; And I tried to repalce the i7 5820K with i7 6800K, the problem is gone, there is no performance drop.
What could be the cause of the problem? Where should I look to solve it?
Thank you.
Dramaticlly slow down after patch of Meltdown
Re: Dramaticlly slow down after patch of Meltdown
Try toggling the 3 switches that control the new code and see which one makes the most difference. Look at the files /sys/kernel/debug/x86/*enabled - should be 3 of them, ibpb, ibrs and pti_enabled. First run cat /sys/kernel/debug/x86/*enabled and see what the current values are. You can change them by using e.g. echo 0 > /sys/kernel/debug/x86/pti_enabled
If ibrs_enabled=1 on my work machines then it doubles cpu usage.
If ibrs_enabled=1 on my work machines then it doubles cpu usage.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke
Re: Dramaticlly slow down after patch of Meltdown
Thanks a lot, finally find the real culprit. the performance drop is due to the ibrs_enable, disable it turns the performance back.TrevorH wrote:Try toggling the 3 switches that control the new code and see which one makes the most difference. Look at the files /sys/kernel/debug/x86/*enabled - should be 3 of them, ibpb, ibrs and pti_enabled. First run cat /sys/kernel/debug/x86/*enabled and see what the current values are. You can change them by using e.g. echo 0 > /sys/kernel/debug/x86/pti_enabled
If ibrs_enabled=1 on my work machines then it doubles cpu usage.
Tried 4790/4790K/5820K/6700K/6800K/E5 2690, only 5820K is affected, it is strange.
Re: Dramaticlly slow down after patch of Meltdown
Check the output from dmesg on each of those processors and see which ones have microcode that support IBRS. I suspect that only the one that slows down is using the latest. Like this
That's on a VM and shows that there is no microcode that supports the IBRS mitigation. On a machine with fixed microcode it should say
[339488.642229] FEATURE SPEC_CTRL Present
[339488.642231] FEATURE IBPB_SUPPORT Present
Code: Select all
[root@centos7 ~]# dmesg | grep FEAT
[ 0.116718] FEATURE SPEC_CTRL Not Present
[ 0.117258] FEATURE IBPB_SUPPORT Not Present
[339488.642229] FEATURE SPEC_CTRL Present
[339488.642231] FEATURE IBPB_SUPPORT Present
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke
Re: Dramaticlly slow down after patch of Meltdown
Yes, you are right, the 5820K is the only one with updated microcode, we are doomed. Updating the microcode will affect all systems.TrevorH wrote: That's on a VM and shows that there is no microcode that supports the IBRS mitigation. On a machine with fixed microcode it should say
Re: Dramaticlly slow down after patch of Meltdown
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke