Date: Mon, 26 Nov 2012 00:36:03 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: Alex Chistyakov <alexclear@gmail.com> Cc: "freebsd-emulation@freebsd.org" <freebsd-emulation@FreeBSD.org>, Alexander Motin <mav@FreeBSD.org> Subject: Re: VirtualBox 4.2.4 on FreeBSD 9.1-PRERELEASE problem: VMs behave very different when pinned to different cores Message-ID: <50B29D53.5080802@FreeBSD.org> In-Reply-To: <50B25C17.20208@FreeBSD.org> References: <CA%2Bkq2xvh3j5CM7UzRVfXCeLhHwpTY%2B_M7dCJx0c27NtV8EVJwg@mail.gmail.com> <CAE-m3X1UPsy%2Bwbqm_02JpXMr-UO3m7N6z_ZwY2HNo4GL0YUi1w@mail.gmail.com> <CA%2Bkq2xva61m_bHdzBZM2TYL5z7XiohvkxsYWtOyoBwQkpyvp0A@mail.gmail.com> <50AFAD05.1050604@FreeBSD.org> <CA%2Bkq2xv%2BU4ZnfK=1js4PRaNpTNdW-y-G50GV4%2BMVP0LugBf1pQ@mail.gmail.com> <50B25C17.20208@FreeBSD.org>
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on 25/11/2012 19:57 Andriy Gapon said the following: > on 24/11/2012 00:17 Alex Chistyakov said the following: >> I collected two samples and put them here: http://1888.spb.ru/samples.zip >> sched-cpu0.ktr is for a VM running on CPU #0 and sched-cpu1.ktr is for >> a VM running on CPU #1 >> They seem to be very different. > > It looks like you didn't stop ktr tracing before running ktrdump or something > like that. schedgraph can not grok the files because it believes that the > timestamps are incorrect. > > # - While the workload is continuing (i.e. before it finishes), disable > # KTR tracing by setting 'sysctl debug.ktr.mask=0'. This is necessary > # to avoid a race condition while running ktrdump, i.e. the KTR ring buffer > # will cycle a bit while ktrdump runs, and this confuses schedgraph because > # the timestamps appear to go backwards at some point. Hmm, looks like this assessment is not correct. I now think that the root cause of schedgraph issue might be a too wild difference in what TSC counters produce on different (logical/physical) CPUs. E.g.: 131059 1 33232414877586 ... 131058 1 33232414876546 ... 131057 3 33232416064514 ... 131056 3 33232416064198 ... Or even: 131038 0 33232862369416 ... 131037 3 33232409671570 ... 131036 0 33232862367256 ... 131035 3 33232409670982 ... That's 455111586 ticks! > Could you please also provide the CPU identification block from dmesg? This is even more interesting now. -- -- Andriy Gapon
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