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From: David Ahern <dsahern@gmail.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Perf Users <linux-perf-users@vger.kernel.org>
Subject: perf probe and bitfields
Date: Fri, 19 Jan 2018 08:43:50 -0800	[thread overview]
Message-ID: <52f06b83-1065-dc88-756e-7f8fffc5c21e@gmail.com> (raw)

Hi Arnaldo / Masami:

Are there known issues / limitations with perf probe and bitfields?

Here's an example: pkt_type is a bitfield in sk_buff. When I put a probe
in arp_rcv to examine the pkt_type value:

$ perf probe 'arp_rcv ptype=skb->pkt_type dev=dev->name:string'

I only get '0' output:

$ perf script
     vhost-27472 27483 [013] 4313207.619714: probe:arp_rcv:
(ffffffff815653b0) ptype=0 dev="br1"
     vhost-27472 27483 [013] 4313207.619763: probe:arp_rcv:
(ffffffff815653b0) ptype=0 dev="br1"
     vhost-27472 27483 [013] 4313210.588990: probe:arp_rcv:
(ffffffff815653b0) ptype=0 dev="br1"

when I know broadcast packet are getting handled (pkt_type ==
PACKET_BROADCAST). This is confirmed by adding a printk to arp_rcv.

Thanks,
David

             reply	other threads:[~2018-01-19 16:43 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-19 16:43 David Ahern [this message]
2018-01-26  6:56 ` perf probe and bitfields Namhyung Kim
2018-01-26 16:28   ` David Ahern
2018-01-27  5:04     ` Masami Hiramatsu
2018-01-30 16:53       ` David Ahern

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