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

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Message-ID: <20181101085951.GD3159@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Nov 2018 09:59:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yi Sun <yi.y.sun@...ux.intel.com>
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 Thu, Nov 01, 2018 at 11:20:21AM +0800, Yi Sun wrote:
> On 18-10-31 18:15:39, Peter Zijlstra wrote:

> > So Yi, are you actually seeing a problem? If so, can you give details?
> 
> Where does the patch come from? I cannot find it through google.

What patch!? The one I posted:

  https://lkml.kernel.org/r/20181031141030.GB13219@hirez.programming.kicks-ass.net

I made that up real quick.

> Per Waiman's comment, it seems not suitable to call vcpu_is_preempted()
> in pv_wait_head_or_lock(). So, we cannot make HvSpinWaitInfo notification
> through vcpu_is_preempted() for such case. Based on that, I suggest to
> add one more callback function in pv_lock_ops.

We're not doing anything until you can show a problem. If it ain't
broken, don't fix it etc..

> BTW, which performance test do you suggest? I am trying to test it by
> AIM7.

Waiman?