> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] > Sent: Tuesday, February 14, 2017 4:44 AM > To: x86@xxxxxxxxxx; Andy Lutomirski <luto@xxxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; > H. Peter Anvin <hpa@xxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; > Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger > <sthemmin@xxxxxxxxxxxxx>; Dexuan Cui <decui@xxxxxxxxxxxxx>; linux- > kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; > virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx > Subject: [PATCH v2 0/3] x86/vdso: Add Hyper-V TSC page clocksource support > > Hi, > > while we're still waiting for a definitive ACK from Microsoft that the algorithm > is good for SMP case (as we can't prevent the code in vdso from migrating > between CPUs) I'd like to send v2 with some modifications to keep the > discussion going. I checked with the folks on the Hyper-V side and they have confirmed that we need to add memory barriers in the guest code to ensure the various reads from the TSC page are correctly ordered - especially, the initial read of the sequence counter must have acquire semantics. We should ensure that other reads from the TSC page are completed before the second read of the sequence counter. I am working with the Windows team to correctly reflect this algorithm in the Hyper-V specification. Regards, K. Y > > Changes since v1: > - Document the TSC page reading protocol [Thomas Gleixner]. > > - Separate the TSC page reading code from read_hv_clock_tsc() and put it to > asm/mshyperv.h to use from both hv_init.c and vdso. > > - Add explicit barriers [Thomas Gleixner] > > Original description: > > Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol > defined by the hypervisor is different from VCLOCK_PVCLOCK. Implemented > the required support. Simple sysbench test shows the following results: > > Before: > # time sysbench --test=memory --max-requests=500000 run ... > real 1m22.618s > user 0m50.193s > sys 0m32.268s > > After: > # time sysbench --test=memory --max-requests=500000 run ... > real 0m47.241s > user 0m47.117s > sys 0m0.008s > > Patches 1 and 2 are made on top of K. Y.'s code refactoring which moved tsc > page clocksource to arch/x86/hyperv/hv_init.c, this is currently present in > Greg's char-misc-next tree. > > Vitaly Kuznetsov (3): > x86/hyperv: implement hv_get_tsc_page() > x86/hyperv: move TSC reading method to asm/mshyperv.h > x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method > > arch/x86/entry/vdso/vclock_gettime.c | 24 +++++++++++++++ > arch/x86/entry/vdso/vdso-layout.lds.S | 3 +- > arch/x86/entry/vdso/vdso2c.c | 3 ++ > arch/x86/entry/vdso/vma.c | 7 +++++ > arch/x86/hyperv/hv_init.c | 48 +++++++++-------------------- > arch/x86/include/asm/clocksource.h | 3 +- > arch/x86/include/asm/mshyperv.h | 58 > +++++++++++++++++++++++++++++++++++ > arch/x86/include/asm/vdso.h | 1 + > drivers/hv/Kconfig | 3 ++ > 9 files changed, 114 insertions(+), 36 deletions(-) > > -- > 2.9.3 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
