linux-kernel - Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall

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Date:   Mon, 22 Oct 2018 09:53:42 +0800
From:   Yi Sun <yi.y.sun@...ux.intel.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        chao.p.peng@...el.com, chao.gao@...el.com,
        isaku.yamahata@...el.com, michael.h.kelley@...rosoft.com,
        tianyu.lan@...rosoft.com, "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall

On 18-10-19 16:20:52, Juergen Gross wrote:
> On 19/10/2018 15:13, Yi Sun wrote:

[...]

> > diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> > index 0130e48..9e88c7e 100644
> > --- a/kernel/locking/qspinlock_paravirt.h
> > +++ b/kernel/locking/qspinlock_paravirt.h
> > @@ -7,6 +7,8 @@
> >  #include <linux/bootmem.h>
> >  #include <linux/debug_locks.h>
> >  
> > +#include <asm/mshyperv.h>
> > +
> >  /*
> >   * Implement paravirt qspinlocks; the general idea is to halt the vcpus instead
> >   * of spinning them.
> > @@ -305,6 +307,10 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
> >  				wait_early = true;
> >  				break;
> >  			}
> > +#if defined(CONFIG_X86_64) && defined(CONFIG_PARAVIRT_SPINLOCKS) && IS_ENABLED(CONFIG_HYPERV)
> > +			if (!hv_notify_long_spin_wait(SPIN_THRESHOLD - loop))
> > +				break;
> > +#endif
> 
> I don't like that. Why should a KVM or Xen guest call into a hyperv
> specific function?
> 
> Can't you move this to existing hyperv specific paravirt hooks?
> 
hv_notify_long_spin_wait() must be called in this loop but it seems
there is no appropriate existing paravirt hook here. So, can I add
one more hook in pv_lock_ops to do this notification?

> 
> Juergen