Re: [PATCH] Implement timekeeping for rumprun/hw (x86)

  • From: Antti Kantee <pooka@xxxxxx>
  • To: rumpkernel-users@xxxxxxxxxxxxx
  • Date: Mon, 06 Jul 2015 17:00:27 +0000

On 06/07/15 16:50, Martin Lucina wrote:

On Monday, 06.07.2015 at 16:41, Antti Kantee wrote:
On 06/07/15 14:43, Martin Lucina wrote:
I have also put in a check that warns if the "TSC invariant" bit is not set
in CPUID, however it turns out that neither KVM nor QEMU set this on my
system, possibly on purpose. So halting if that flag is not set would not
be very useful :-/

Doesn't QEMU set the flags based on which cpu you tell it to
emulate? Or are you saying the flag is stripped even if the host cpu
sets it and -cpu host is used?

The latter. It seems there's some work happened recently-ish regarding
this. Under "KVM" in http://wiki.qemu.org/ChangeLog/2.1:

New "invtsc" (Invariant TSC) CPU feature. When enabled, this will block
migration and savevm, so it is not enabled by default on any CPU model. To enable invtsc,
the migratable=no flag (supported only by -cpu host, by now) is required. So, invtsc is
available only if using: -cpu host,migratable=no,+invtsc.

I did try "-cpu host,migratable=no,+invtsc" on my machine but it doesn't
make the warning go away...

Silly question, but gotta ask it: is there a system where the warning doesn't trigger?

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