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From: Steven Rostedt <rostedt@goodmis.org>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
	Paul Mackerras <paulus@ozlabs.org>,
	linuxppc-dev@lists.ozlabs.org,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Anton Blanchard <anton@samba.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	sathnaga@linux.vnet.ibm.com
Subject: Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
Date: Mon, 19 Mar 2018 10:13:44 -0400	[thread overview]
Message-ID: <20180319101344.72144f30@gandalf.local.home> (raw)
In-Reply-To: <cdbe15845a5da965878b6344f69b6ed6dbabb87b.1521449527.git.naveen.n.rao@linux.vnet.ibm.com>

On Mon, 19 Mar 2018 14:43:00 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> index 3f3e81852422..fdf702b4df25 100644
> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> @@ -60,6 +60,19 @@ _GLOBAL(ftrace_caller)
>  	mfxer   r10
>  	mfcr	r11
>  
> +#ifdef CONFIG_KVM
> +	lbz	r3, PACA_FTRACE_DISABLED(r13)
> +	cmpdi	r3, 0
> +	beq	1f
> +	mflr	r3
> +	mtctr	r3
> +	REST_GPR(3, r1)
> +	addi	r1, r1, SWITCH_FRAME_SIZE
> +	mtlr	r0
> +	bctr
> +1:
> +#endif

I wonder if we should try to move the return out of the fast path (for
cache reasons), as most of the time the above compare will be true. That
is:

#ifdef CONFIG_KVM
	lbz	r3, PACA_FTRACE_DISABLED(r13)
	cmpdi	r3, 0
	bne	no_trace
#endif

/* rest of ftrace_caller code */

/* after ftrace_caller... */
        bctr                    /* jump after _mcount site */

#ifdef	CONFIG_KVM
no_trace:
	mflr	r3
	mtctr	r3
	REST_GPR(3, r1)
	addi	r1, r1, SWITCH_FRAME_SIZE
	mtlr	r0
	bctr
#endif


-- Steve

> +
>  	/* Get the _mcount() call site out of LR */
>  	mflr	r7
>  	/* Save it as pt_regs->nip */

  parent reply	other threads:[~2018-03-19 14:13 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-19  9:12 [PATCH 0/2] Disable ftrace during kvm guest entry/exit Naveen N. Rao
2018-03-19  9:13 ` [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Naveen N. Rao
2018-03-19 10:40   ` Nicholas Piggin
2018-03-19 18:53     ` Naveen N. Rao
2018-03-19 22:34     ` Michael Ellerman
2018-03-20  0:05       ` Nicholas Piggin
2018-03-20 11:02       ` Naveen N. Rao
2018-03-19 14:13   ` Steven Rostedt [this message]
2018-03-19 18:54     ` Naveen N. Rao
2018-03-19  9:13 ` [PATCH 2/2] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit Naveen N. Rao

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