linux-kernel - Re: [v4,6/6] powerpc: kprobes: prefer ftrace when probing function entry

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Date:   Tue, 25 Apr 2017 08:47:33 +1000 (AEST)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [v4,6/6] powerpc: kprobes: prefer ftrace when probing function entry

On Wed, 2017-04-19 at 12:52:28 UTC, "Naveen N. Rao" wrote:
> KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it
> eliminates the need for a trap, as well as the need to emulate or
> single-step instructions.
> 
> Though OPTPROBES provides us with similar performance, we have limited
> optprobes trampoline slots. As such, when asked to probe at a function
> entry, default to using the ftrace infrastructure.
> 
> With:
> 	# cd /sys/kernel/debug/tracing
> 	# echo 'p _do_fork' > kprobe_events
> 
> before patch:
> 	# cat ../kprobes/list
> 	c0000000000daf08  k  _do_fork+0x8    [DISABLED]
> 	c000000000044fc0  k  kretprobe_trampoline+0x0    [OPTIMIZED]
> 
> and after patch:
> 	# cat ../kprobes/list
> 	c0000000000d074c  k  _do_fork+0xc    [DISABLED][FTRACE]
> 	c0000000000412b0  k  kretprobe_trampoline+0x0    [OPTIMIZED]
> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/24bd909e94776ecce95291bff910f1

cheers