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From: Jeff Moyer <jmoyer@redhat.com>
To: jens.axboe@fusionio.com
Cc: linux-kernel@vger.kernel.org
Subject: blk_classic tracing horribly broken
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Date: Thu, 22 Sep 2011 13:57:11 -0400
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Hi,

I've stared at the code for a while, and I've come up empty.  Would
anyone care to take a stab at fixing this?

To reproduce:

mount -t debugfs none /sys/kernel/debug
cd /sys/kernel/debug/tracing
echo blk > current_tracer
echo 1 > events/block/enable
echo 1 > options/blk_classic
echo 1 > tracing_on

dd if=/dev/<device> of=/dev/null bs=1M count=1 iflag=direct
cat trace

This is what I see:

# tracer: blk
#
# DEV   CPU TIMESTAMP     PID ACT FLG
#  |     |     |           |   |   |
Unknown action 52
Unknown action 52
Unknown action bce
Unknown action 52
Unknown action 52
Unknown action 52
Unknown action 52
Unknown action 52
Unknown action 52
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
  0,0    2   110.941937315  2584  F   R [pgrep]
Unknown action 52
Unknown action 52
Unknown action 231
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
  0,0    0   110.949383287  2584  F   R [pgrep]
Unknown action 52
Unknown action 52
Unknown action 7fd1
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
  0,0    3   110.984565328  2581  F   R [ps]
Unknown action 52
Unknown action 52
Unknown action 5ad1
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0
  0,0    3   111.003843579  2581  F   R [ps]
Unknown action 52
Unknown action 52
Unknown action 7551
Unknown action 0
Unknown action 0
Unknown action 0
Unknown action 0

Cheers,
Jeff