From: Yi Sun <yi.y.sun@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
chao.p.peng@intel.com, chao.gao@intel.com,
isaku.yamahata@intel.com, michael.h.kelly@microsoft.com,
tianyu.lan@microsoft.com, "K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>
Subject: Re: [PATCH v1 2/3] locking/pvqspinlock, hv: Enable PV qspinlock for Hyper-V
Date: Thu, 20 Sep 2018 09:56:44 +0800 [thread overview]
Message-ID: <20180920015644.GE11769@yi.y.sun> (raw)
In-Reply-To: <20180917125452.GC11769@yi.y.sun>
Hi,
On 18-09-17 20:54:52, Yi Sun wrote:
> On 18-09-14 12:42:33, Thomas Gleixner wrote:
> > On Fri, 14 Sep 2018, Yi Sun wrote:
> > > > > +static void hv_notify_long_spin_wait(void)
> > > > > +{
> > > > > + u64 input = spin_wait_info | 0x00000000ffffffff;
> > > >
> > > > What? The result is always 0x00000000ffffffff .....
> > > >
> > > Oh, sorry for such error.
> > >
> > > > > + spin_wait_info++;
> > > > > + hv_do_fast_hypercall8(HVCALL_NOTIFY_LONG_SPIN_WAIT, input);
> > > > > +}
> > > > > +
> > > > > +static void hv_qlock_kick(int cpu)
> > > > > +{
> > > > > + spin_wait_info--;
> > > >
> > > > Looking at the above this is completely pointless and I have no idea what
> > > > that variable is supposed to do.
> > > >
> > > Per Microsoft Hypervisor Top Level Functional Specification, the input
> > > parameter of HVCALL_NOTIFY_LONG_SPIN_WAIT is defined as below:
> > >
> > > SpinwaitInfo – Specifies the accumulated count the guest was spinning.
> > >
> > > So, it is increased when guest is spinning and reduced when spinlock is
> > > released.
> >
> > But that's a global variable, so it might be incremented and decremented by
> > several CPUs at once. I don't have the spec and have no time to study it
> > either, but global does not make any sense to me. The spin wait info comes
> > from a single guest CPU and the wakeup is targeted at that guest CPU as
> > well. So why global? It might be defined that way, but then you really want
> > to explain it proper.
> >
> > Thanks,
> >
> > tglx
> >
> Let me check this more. Will reply to you later. Thanks!
>
> BRs,
> Yi Sun
I have got the details from Microsoft.
Notify_Long_Spin_Wait hypercall should be called after a specific times
spinning which can be got through CPUID. When hypervisor receives this,
it will try to ensure that all vcpus are scheduled.
Notify_Long_Spin_Wait is a standalone feature which should be split out
as a new patch set.
So I would like split it into a new patch set and submit it after PV
Hyper-V Spinlock patch set merged.
next prev parent reply other threads:[~2018-09-20 1:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-13 9:13 [PATCH v1 0/3] Enable PV qspinlock for Hyper-V Yi Sun
2018-09-13 9:13 ` [PATCH v1 1/3] X86/Hyper-V: Add Guest IDLE MSR support Yi Sun
2018-09-13 9:13 ` [PATCH v1 2/3] locking/pvqspinlock, hv: Enable PV qspinlock for Hyper-V Yi Sun
2018-09-13 11:06 ` Thomas Gleixner
2018-09-14 8:53 ` Yi Sun
2018-09-13 11:24 ` Thomas Gleixner
2018-09-14 9:04 ` Yi Sun
2018-09-14 10:42 ` Thomas Gleixner
2018-09-17 12:54 ` Yi Sun
2018-09-20 1:56 ` Yi Sun [this message]
2018-09-13 16:16 ` kbuild test robot
2018-09-13 16:42 ` kbuild test robot
2018-09-13 9:13 ` [PATCH v1 3/3] hv: add description for hv_nopvspin Yi Sun
2018-09-15 23:43 ` [PATCH v1 0/3] Enable PV qspinlock for Hyper-V Michael Kelley (EOSG)
2018-09-17 14:37 ` Yi Sun
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