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From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Oscar Salvador <osalvador@suse.de>,
	Ingo Molnar <mingo@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	linux-doc@vger.kernel.org, Waiman Long <longman@redhat.com>
Subject: Re: [PATCH resend] x86,kvm: Add a kernel parameter to disable PV spinlock
Date: Mon, 4 Sep 2017 15:21:57 -0700	[thread overview]
Message-ID: <20170904222157.GD17982@linux-80c1.suse> (raw)
In-Reply-To: <20170904144011.gp7hpis6usjehbuf@hirez.programming.kicks-ass.net>

On Mon, 04 Sep 2017, Peter Zijlstra wrote:

>For testing its trivial to hack your kernel and I don't feel this is
>something an Admin can make reasonable decisions about.
>
>So why? In general less knobs is better.

+1.

Also, note how b8fa70b51aa (xen, pvticketlocks: Add xen_nopvspin parameter
to disable xen pv ticketlocks) has no justification as to why its wanted
in the first place. The only thing I could find was from 15a3eac0784
(xen/spinlock: Document the xen_nopvspin parameter):

"Useful for diagnosing issues and comparing benchmarks in over-commit CPU scenarios."

So I vote for no additional knobs, specially for such core code.

Thanks,
Davidlohr

  parent reply	other threads:[~2017-09-04 22:21 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-04 14:28 [PATCH resend] x86,kvm: Add a kernel parameter to disable PV spinlock Oscar Salvador
2017-09-04 14:40 ` Peter Zijlstra
2017-09-04 19:32   ` Waiman Long
2017-09-04 22:21   ` Davidlohr Bueso [this message]
2017-09-05  6:28     ` Juergen Gross
2017-09-05  6:57       ` Oscar Salvador
2017-09-05  8:07         ` Peter Zijlstra
2017-09-05  6:58       ` Peter Zijlstra
2017-09-05  7:35         ` Juergen Gross
2017-09-05  8:10           ` Peter Zijlstra
2017-09-05  8:14             ` Juergen Gross
2017-09-05  8:28               ` Peter Zijlstra
2017-09-05  8:52                 ` Juergen Gross
2017-09-05  9:03                   ` Peter Zijlstra
2017-09-05  9:11                     ` Juergen Gross

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