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[Xen-devel] Re: [PATCH 00/13] [PATCH RFC] Paravirtualized ticketlocks

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 00/13] [PATCH RFC] Paravirtualized ticketlocks
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 2 Sep 2011 13:27:44 -0700
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, KVM <kvm@xxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Fri, Sep 2, 2011 at 1:07 PM, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
>
> I don't know whether that fastpath code is small enough to consider
> inlining everywhere?

No.

There's no point in inlining something that ends up containing a
conditional function call: gcc will have to effectively save/restore
registers around that thing anyway, so you lose a lot of the
advantages of inlining. So I think it's better done as an out-of-line
function, which I thought we did for spinlocks anyway.

Also, do you run with CONFIG_OPTIMIZE_SIZE? Without that, gcc should
be smart enough to make a "likely()" case be a fall-through.

                          Linus

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