Re: [PATCH] block: introduce block_io_start/block_io_done tracepoints

[Francis Laniel <flaniel@linux.microsoft.com>]

Hi.


Le vendredi 14 octobre 2022, 12:01:11 CEST Hengqi Chen a écrit :
> Currently, several BCC ([0]) tools (biosnoop/biostacks/biotop) use
> kprobes to blk_account_io_start/blk_account_io_done to implement
> their functionalities. This is fragile because the target kernel
> functions may be renamed ([1]) or inlined ([2]). So introduces two
> new tracepoints for such use cases.

Thank you for working on this, I was able to build a kernel with your patch 
and successfully tested it:
root@vm-amd64:~# uname -a
Linux vm-amd64 6.0.0-rc4-00001-g89f38605b66b #95 SMP PREEMPT_DYNAMIC Fri Oct 
14 18:03:58 CEST 2022 x86_64 GNU/Linux
root@vm-amd64:~# perf_5.10 record -e block:block_io_done -e 
block:block_io_start -a dd if=/dev/zero of=foo count=100
...
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.083 MB perf.data (1 samples) ]
root@vm-amd64:~# perf_5.10 script                                              
              dd   313 [000]   273.355898: block:block_io_start: 8,0 W 53248 
()>
         swapper     0 [000]   273.357048:  block:block_io_done: 8,0 W 0 () 
484>

So, I can offer you this:
Tested-by: Francis Laniel <flaniel@linux.microsoft.com>

>   [0]: https://github.com/iovisor/bcc
>   [0]: https://github.com/iovisor/bcc/issues/3954
>   [1]: https://github.com/iovisor/bcc/issues/4261

One small nit:
[0]: https://github.com/iovisor/bcc
[1]: https://github.com/iovisor/bcc/issues/3954
[2]: https://github.com/iovisor/bcc/issues/4261

> 
> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> ---
>  block/blk-mq.c               |  4 ++++
>  include/trace/events/block.h | 27 ++++++++++++++++++++++++++-
>  2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index c96c8c4f751b..3777f486a365 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -887,6 +887,8 @@ static void __blk_account_io_done(struct request *req,
> u64 now)
> 
>  static inline void blk_account_io_done(struct request *req, u64 now)
>  {
> +	trace_block_io_done(req);
> +
>  	/*
>  	 * Account IO completion.  flush_rq isn't accounted as a
>  	 * normal IO on queueing nor completion.  Accounting the
> @@ -917,6 +919,8 @@ static void __blk_account_io_start(struct request *rq)
> 
>  static inline void blk_account_io_start(struct request *req)
>  {
> +	trace_block_io_start(req);
> +
>  	if (blk_do_io_stat(req))
>  		__blk_account_io_start(req);
>  }
> diff --git a/include/trace/events/block.h b/include/trace/events/block.h
> index 7f4dfbdf12a6..65c4cb224736 100644
> --- a/include/trace/events/block.h
> +++ b/include/trace/events/block.h
> @@ -245,6 +245,32 @@ DEFINE_EVENT(block_rq, block_rq_merge,
>  	TP_ARGS(rq)
>  );
> 
> +/**
> + * block_io_start - insert a request for execution
> + * @rq: block IO operation request
> + *
> + * Called when block operation request @rq is queued for execution
> + */
> +DEFINE_EVENT(block_rq, block_io_start,
> +
> +	TP_PROTO(struct request *rq),
> +
> +	TP_ARGS(rq)
> +);
> +
> +/**
> + * block_io_done - block IO operation request completed
> + * @rq: block IO operation request
> + *
> + * Called when block operation request @rq is completed
> + */
> +DEFINE_EVENT(block_rq, block_io_done,
> +
> +	TP_PROTO(struct request *rq),
> +
> +	TP_ARGS(rq)
> +);
> +
>  /**
>   * block_bio_complete - completed all work on the block operation
>   * @q: queue holding the block operation
> @@ -556,4 +582,3 @@ TRACE_EVENT(block_rq_remap,
> 
>  /* This part must be outside protection */
>  #include <trace/define_trace.h>
> -


Best regards.