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Subject: Re: Ping: [PATCH v15 00/13] support "task_isolation" mode
To: Chris Metcalf <cmetcalf@mellanox.com>,
        Gilad Ben Yossef <giladb@mellanox.com>,
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From: Francis Giraldeau <francis.giraldeau@gmail.com>
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Date: Wed, 7 Sep 2016 17:39:26 -0400
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On 2016-09-07 05:11 PM, Francis Giraldeau wrote:
> The syscall test fails on x86:
>     $ sudo ./isolation
>     [...]
>     test_syscall: FAIL (0x100)
>     test_syscall (SIGUSR1): FAIL (0x100)
>
> I wanted to debug this problem with gdb and a KVM virtual machine. However, the TSC clock source is detected as non reliable, even with the boot parameter tsc=reliable, and therefore prctl(PR_SET_TASK_ISOLATION, PR_TASK_ISOLATION_ENABLE) always returns EAGAIN. Is there a trick to run task isolation in a VM (at least for debugging purposes)?

OK, got it. The guest kernel must be compiled with CONFIG_KVM_GUEST, and then with virsh edit, set the clock configuration of the VM (under <domain>):

 <clock offset='utc'>
    <timer name='kvmclock'/>
  </clock>

Of course, the jitter is horrible, but at least it is possible to debug with GDB.

Cheers,

Francis