Re: [PATCH] blkparse: Fix blktrace output pipe broken in the new

[Jens Axboe <axboe@kernel.dk>]

On 2011-01-11 07:48, Tao Ma wrote:
> From: Tao Ma <boyu.mt@taobao.com>
> 
> 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.

But I'm curious, this is a 2.6.37 regression?


-- 
Jens Axboe