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From: Waiman Long <longman@redhat.com>
To: Juergen Gross <jgross@suse.com>, Yi Sun <yi.y.sun@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de,
	chao.p.peng@intel.com, chao.gao@intel.com,
	isaku.yamahata@intel.com, michael.h.kelley@microsoft.com,
	tianyu.lan@microsoft.com, "K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"mingo@redhat.com" <mingo@redhat.com>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall
Date: Mon, 22 Oct 2018 12:31:45 -0400	[thread overview]
Message-ID: <ba75b994-c1a6-6e91-6499-b9af90636fcf@redhat.com> (raw)
In-Reply-To: <2e0d62cb-b706-a5b4-65f7-982a913fb32b@suse.com>

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
>>> 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?
> 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.
>
> Adding some more locking maintainers and Waiman to the Cc: list.
>
>
> Juergen
>
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.

Cheers,
Longman



  reply	other threads:[~2018-10-22 16:31 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-19 13:13 [PATCH v1 0/2] Enable HvNotifyLongSpinWait for Hyper-V Yi Sun
2018-10-19 13:13 ` [PATCH v1 1/2] x86/hyperv: get spinlock retry number on Hyper-V Yi Sun
2018-10-19 13:13 ` [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall Yi Sun
2018-10-19 14:20   ` Juergen Gross
2018-10-22  1:53     ` Yi Sun
2018-10-22  7:32       ` Juergen Gross
2018-10-22 16:31         ` Waiman Long [this message]
2018-10-22 17:15           ` Peter Zijlstra
2018-10-22 17:27             ` Waiman Long
2018-10-22 17:31               ` Peter Zijlstra
2018-10-22 18:01                 ` Waiman Long
2018-10-23  2:57             ` Yi Sun
2018-10-23  8:51               ` Peter Zijlstra
2018-10-23  9:33                 ` Yi Sun
2018-10-31  1:54                   ` Yi Sun
2018-10-31 14:10                     ` Peter Zijlstra
2018-10-31 15:07                       ` Waiman Long
2018-10-31 17:15                         ` Peter Zijlstra
2018-11-01  3:20                           ` Yi Sun
2018-11-01  8:59                             ` Peter Zijlstra
2018-11-01 12:59                             ` Waiman Long
2018-11-05  6:54                               ` Yi Sun
2018-10-24 16:53   ` Michael Kelley
2018-10-25  2:23     ` Yi Sun
2018-10-31  2:06     ` Yi Sun

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