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From: "Wu, Wentong" <wentong.wu@intel.com>
To: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: [Qemu-devel] qemu icount mode timer accuracy
Date: Fri, 9 Aug 2019 04:00:20 +0000	[thread overview]
Message-ID: <228A20DABA3D9846AF1B64E31C217296010E8CE3@SHSMSX106.ccr.corp.intel.com> (raw)


Hi,

Recently I'm working to enable Qemu icount mode with TCG, with source code review I found that Qemu can give deterministic execution for guest code timeout. But for exact time point for guest OS, I have a question:

For armv7m_systick.c example, guest OS will use systick_read which will call "t = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); " to calculate his exact time point, and qemu_clock_get_ns will use qemu_icount. But from qemu_tcg_rr_cpu_thread_fn { prepare_icount_for_run(cpu); r = tcg_cpu_exec(cpu); process_icount_data(cpu);}, we know qemu just update qemu_icount value after tcg_cpu_exec, so for each tcg_cpu_exec execution there is the same qemu_icount value, and then guest code will get the same time point for that one tcg execution. Can someone confirm that?



Thanks

             reply	other threads:[~2019-08-09  4:01 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-09  4:00 Wu, Wentong [this message]
2019-08-19 20:49 [Qemu-devel] qemu icount mode timer accuracy Wu, Wentong
2019-08-19 21:14 Wu, Wentong

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