Commit Graph

2 Commits

Author SHA1 Message Date
Luiz Capitulino 4f5758fc67 kvm: x86: export TSC information to user-space
This commit exports the following information to
user-space via the newly created per-vcpu debugfs
directory:

 - TSC offset (as a signed number)
 - TSC scaling ratio
 - TSC scaling ratio fractinal bits

The original intention of this commit was to
export only the TSC offset, but the TSC scaling
information is exported for completeness.

We need to retrieve the TSC offset from user-space
in order to support the merging of host and guest
traces in trace-cmd. Today, we use the kvm_write_tsc_offset
tracepoint, but it has a number of problems (mainly,
it requires a running VM to be rebooted, ftrace setup,
and also tracepoints are not supposed to be ABIs).

The merging of host and guest traces is explained
in more detail in this thread:

 [Qemu-devel] [RFC] host and guest kernel trace merging
 https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg00887.html

This commit creates the following files in debugfs:

/sys/kernel/debug/kvm/66828-10/vcpu0/tsc-offset
/sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio
/sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio-frac-bits

The last two are only created if TSC scaling is supported.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-09-16 16:57:48 +02:00
Luiz Capitulino 235539b48a kvm: add stubs for arch specific debugfs support
Two stubs are added:

 o kvm_arch_has_vcpu_debugfs(): must return true if the arch
   supports creating debugfs entries in the vcpu debugfs dir
   (which will be implemented by the next commit)

 o kvm_arch_create_vcpu_debugfs(): code that creates debugfs
   entries in the vcpu debugfs dir

For x86, this commit introduces a new file to avoid growing
arch/x86/kvm/x86.c even more.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-09-16 16:57:47 +02:00