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

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Message-ID: <20181023025740.GL11769@yi.y.sun>
Date:   Tue, 23 Oct 2018 10:57:40 +0800
From:   Yi Sun <yi.y.sun@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, Juergen Gross <jgross@...e.com>,
        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>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall

On 18-10-22 19:15:16, Peter Zijlstra wrote:
> 
> Firstly, who come a patch that is grubbing around in kernel/locking/ has
> an x86/hyperv subject and isn't Cc'ed to the locking maintainers?
> 
I am sorry. That is my fault to forget to add locking maintainers.

> On Mon, Oct 22, 2018 at 12:31:45PM -0400, Waiman Long wrote:
> > On 10/22/2018 03:32 AM, Juergen Gross wrote:
> > > On 22/10/2018 03:53, Yi Sun wrote:
> > >> 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
> 
> Secondly; how come you thought that was acceptable in any way shape or
> form?
> 
Sorry for that. Will try another way.

> > > vcpu_is_preempted() is already part of this loop. And this is a paravirt
> > > hook. Can't you make use of that? This might require adding another
> > > parameter to this hook, but I'd prefer that over another pv-spinlock
> > > hook.
> 
> > I agree with Juergen on that. I would suggest rename the
> > vcpu_is_preempted hook into a more generic vcpu_stop_spinning, perhaps,
> > so different hypervisors can act on the information accordingly. Adding
> > an extra parameter is fine.
> 
> No; no extra parameters. vcpu_is_preempted() is a simple and intuitive
> interface. Why would we want to make it complicated?