e4a0e48886
The 'nx_huge_pages' option, will force any executable page mapping to be performed at 4KiB granularity and requires any existing overlapping huge-page mapping to be also split in 4KiB chunks[1]. This is due to a HW bug that doesn't affect our NFV use-cases. The way a huge-page mapping is dropped is by simply deleting the EPT entry and flushing TLB caches on all affected CPUs. Next vCPU access to that address will trigger an EPT_VIOLATION, which will jump into the host for it to handle the page-fault. In our specific case, this means all isolated CPUs running oslat will hit an EPT_VIOLATION almost exactly at the same time. Which is bad enough already, but, given our systems might have a huge number of isolated CPUs, will also create a lot of contention over the KVM MMU lock. This has been observed to trigger ~100us latency spikes while testing with oslat. So let's disable the 'kvm.nx_huge_pages' module option. [1] see kernel commit b7e8c8303ff28 Resolves: rhbz#1976825 Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
51 lines
1.4 KiB
Bash
Executable file
51 lines
1.4 KiB
Bash
Executable file
#!/bin/sh
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. /usr/lib/tuned/functions
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start() {
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setup_kvm_mod_low_latency
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return 0
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}
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stop() {
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if [ "$1" = "full_rollback" ]; then
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teardown_kvm_mod_low_latency
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fi
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return "$?"
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}
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verify() {
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retval=0
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# set via /etc/modprobe.d/kvm.conf and /etc/modprobe.d/kvm.rt.tuned.conf
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if [ -f /sys/module/kvm/parameters/kvmclock_periodic_sync ]; then
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kps=$(cat /sys/module/kvm/parameters/kvmclock_periodic_sync)
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if [ "$kps" = "N" -o "$kps" = "0" ]; then
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echo " kvmclock_periodic_sync:($kps): disabled: okay"
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else
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echo " kvmclock_periodic_sync:($kps): enabled: expected N(0)"
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retval=1
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fi
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fi
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if [ -f /sys/module/kvm_intel/parameters/ple_gap ]; then
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ple_gap=$(cat /sys/module/kvm_intel/parameters/ple_gap)
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if [ $ple_gap -eq 0 ]; then
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echo " ple_gap:($ple_gap): disabled: okay"
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else
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echo " ple_gap:($ple_gap): enabled: expected 0"
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retval=1
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fi
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fi
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if [ -f /sys/module/kvm/parameters/nx_huge_pages ]; then
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kps=$(cat /sys/module/kvm/parameters/nx_huge_pages)
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if [ "$kps" = "N" -o "$kps" = "0" ]; then
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echo " kvmclock_periodic_sync:($kps): disabled: okay"
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else
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echo " kvmclock_periodic_sync:($kps): enabled: expected N(0)"
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retval=1
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fi
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fi
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return $retval
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}
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process $@
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