Date: Tue, 10 Dec 2019 10:06:26 -0600 From: Eric van Gyzen <eric@vangyzen.net> To: Ryan Stone <rysto32@gmail.com> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: dtrace not working on bhyve VM without invariant_tsc Message-ID: <ECA9F047-FE57-41AE-8DBF-53D56AC1AEB6@vangyzen.net> In-Reply-To: <CAFMmRNz9Cv2Hepi%2BszMn30BBGKEyEcvUQiE-46kEdpxg6rjH9w@mail.gmail.com> References: <CAFMmRNz9Cv2Hepi%2BszMn30BBGKEyEcvUQiE-46kEdpxg6rjH9w@mail.gmail.com>
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> On Dec 9, 2019, at 8:27 PM, Ryan Stone <rysto32@gmail.com> wrote: >=20 > I have a bhyve VM guest on my laptop where dtrace just constantly > aborts whenever I try to use it: >=20 > [rstone@ebpf dtrace]sudo dtrace -s fdcopy.d > Assertion failed: (buf->dtbd_timestamp >=3D first_timestamp), file > = /usr/home/rstone/git/bsd-worktree/ebpf-import/cddl/contrib/opensolaris/lib= /libdtrace/common/dt_consume.c, > line 3026. > Abort trap >=20 > I believe that the problem is caused by dtrace unconditionally using > rdtsc() to implement dtrace_gethrtime(), assuming that the values will > be stable for a given CPU. The VM's vcpus seem to be getting migrated > frequently. >=20 > Should dtrace instead be using the system timecounter? That should > stand a much better chance of being monotonically increasing. I=E2=80=99ve seen TSC issues with OneFS under bhyve on certain CPUs. = Pinning the VM to CPUs 1-N (i.e. avoiding CPU 0) worked around it. You = might try that as a workaround. Eric=
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