linux-kernel - Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check

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Date:	Tue, 5 Jul 2016 17:57:56 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org,
	virtualization@...ts.linux-foundation.org,
	linux-s390 <linux-s390@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, mpe@...erman.id.au,
	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@....com>, will.deacon@....com,
	boqun.feng@...il.com, Davidlohr Bueso <dave@...olabs.net>,
	schwidefsky@...ibm.com
Subject: Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check

Hi Xinhui,
2016-06-28 22:43 GMT+08:00 Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>:
> This is to fix some lock holder preemption issues. Some other locks
> implementation do a spin loop before acquiring the lock itself. Currently
> kernel has an interface of bool vcpu_is_preempted(int cpu). It take the cpu
> as parameter and return true if the cpu is preempted. Then kernel can break
> the spin loops upon on the retval of vcpu_is_preempted.
>
> As kernel has used this interface, So lets support it.
>
> Only pSeries need supoort it. And the fact is powerNV are built into same
> kernel image with pSeries. So we need return false if we are runnig as
> powerNV. The another fact is that lppaca->yiled_count keeps zero on
> powerNV. So we can just skip the machine type.

Lock holder vCPU preemption can be detected by hardware pSeries or
paravirt method?

Regards,
Wanpeng Li