On 01/11/2011 03:36 PM, Jens Axboe wrote:
On 2011-01-11 07:48, Tao Ma wrote:
From: Tao Ma<boyu.mt@xxxxxxxxxx>
With the newest kernel(say 2.6.37, some older one should also have the
similar problem), some cfq messages are added to blktrace, so it makes
the old blkparse broken.
See a simple example:
1. blktrace /dev/sdb -o -|blkparse -i -
2. Run the following command(/dev/sdb1 is mounted at /mnt/test_dir):
dd if=/mnt/test_dir/test of=/dev/null bs=4k count=1 iflag=direct
There are only 2 lines of output there:
8,16 0 1 0.000000000 13183 A R 114759 + 8<- (8,17) 114696
8,16 0 2 0.000000491 13183 Q R 114759 + 8 [dd]
And even we run a command line like:
for((i=0;i<100;i++))do dd if=/mnt/ocfs2/test of=/dev/null bs=4k count=1 iflag=direct;done
We are only given the same 2 lines of output.
While the really one should look like:
8,16 0 1 0.000000000 13319 A R 114759 + 8<- (8,17) 114696
8,16 0 2 0.000000376 13319 Q R 114759 + 8 [dd]
8,16 0 0 0.000005931 0 m N cfq13319 alloced
8,16 0 3 0.000006259 13319 G R 114759 + 8 [dd]
8,16 0 4 0.000007143 13319 P N [dd]
8,16 0 5 0.000007817 13319 I R 114759 + 8 [dd]
8,16 0 0 0.000008491 0 m N cfq13319 insert_request
8,16 0 0 0.000009029 0 m N cfq13319 add_to_rr
...
The main reason is that in show_entries_rb, we test sequences every time,
but actually with some messages like cfq, the sequence number is always
0 which makes the old sequence check refuses all the logs after it.
So only check/store sequence number if it isn't a message.
Thanks for the patch with the nice and detailed description, I have
applied it.
cool.
But I'm curious, this is a 2.6.37 regression?
Oh, I don't have time to look back the git to see whether it is a
regression or not. ;)
But it should be a compatible problem in blkparse and it should be a
problem when we adds cfq tracing to the kernel, a very long time ago I
guess. I just found this recently when I wanted to know more internals
about the blktrace.
Regards,
Tao
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