linux-kernel - Re: [4.2, Regression] Queued spinlocks cause major XFS performance regression

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Message-ID: <CA+55aFzGY3iHUwoQB1He4zag7CrF-_OdpHcpUTYvGC48zrSSYA@mail.gmail.com>
Date:	Mon, 7 Sep 2015 13:45:18 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Davidlohr Bueso <dave@...olabs.net>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Waiman Long <Waiman.Long@...com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [4.2, Regression] Queued spinlocks cause major XFS performance regression

On Sun, Sep 6, 2015 at 11:57 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> Just to continue the argument for arguments sake, the function is named
> 'virt' (not paravirt) and tests the HYPERVISOR CPUID bit. How is that
> not appropriately named?

Well, I think right now one issue is that you can't avoid it, even
when you want pure "raw hardware" spinlocks.

I really think it should at the very least be inside CONFIG_PARAVIRT.
Because it *is* about helping the hypervisor, so really is about
paravirtualization.

So naming is misleading, I think, and the config option situation is
not great. If you act differently under virtualization than you do on
raw hardware, what would you call that? I'd call it "paravirt".

             Linus
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