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Date: Thu, 21 May 2009 18:42:33 -0400 From: Chuck Ebbert <cebbert@...hat.com> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Ingo Molnar <mingo@...e.hu>, "Xin, Xiaohui" <xiaohui.xin@...el.com>, "Li, Xin" <xin.li@...el.com>, "Nakajima, Jun" <jun.nakajima@...el.com>, "H. Peter Anvin" <hpa@...or.com>, Nick Piggin <npiggin@...e.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Xen-devel <xen-devel@...ts.xensource.com> Subject: Re: Performance overhead of paravirt_ops on native identified On Wed, 13 May 2009 17:16:55 -0700 Jeremy Fitzhardinge <jeremy@...p.org> wrote: > Paravirt patching turns all the pvops calls into direct calls, so > _spin_lock etc do end up having direct calls. For example, the compiler > generated code for paravirtualized _spin_lock is: > > <_spin_lock+0>: mov %gs:0xb4c8,%rax > <_spin_lock+9>: incl 0xffffffffffffe044(%rax) > <_spin_lock+15>: callq *0xffffffff805a5b30 > <_spin_lock+22>: retq > > The indirect call will get patched to: > <_spin_lock+0>: mov %gs:0xb4c8,%rax > <_spin_lock+9>: incl 0xffffffffffffe044(%rax) > <_spin_lock+15>: callq <__ticket_spin_lock> > <_spin_lock+20>: nop; nop /* or whatever 2-byte nop */ > <_spin_lock+22>: retq > Can't those calls be changed to jumps? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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