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: Mon, 17 Sep 2018 20:54:52 +0800 [thread overview]
Message-ID: <20180917125452.GC11769@yi.y.sun> (raw)
In-Reply-To: <alpine.DEB.2.21.1809141232260.1473@nanos.tec.linutronix.de>
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
next prev parent reply other threads:[~2018-09-17 12:57 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 [this message]
2018-09-20 1:56 ` Yi Sun
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180917125452.GC11769@yi.y.sun \
--to=yi.y.sun@linux.intel.com \
--cc=chao.gao@intel.com \
--cc=chao.p.peng@intel.com \
--cc=haiyangz@microsoft.com \
--cc=isaku.yamahata@intel.com \
--cc=kys@microsoft.com \
--cc=linux-kernel@vger.kernel.org \
--cc=michael.h.kelly@microsoft.com \
--cc=sthemmin@microsoft.com \
--cc=tglx@linutronix.de \
--cc=tianyu.lan@microsoft.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).