netdev - Re: [PATCH bpf-next v2 3/5] nbd: add tracepoints for send/receive timing

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Date:   Sat, 6 Apr 2019 20:13:56 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Matt Mullins <mmullins@...com>
Cc:     hall@...com, ast@...nel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        linux-block@...r.kernel.org, nbd@...er.debian.org
Subject: Re: [PATCH bpf-next v2 3/5] nbd: add tracepoints for send/receive
 timing

On Fri, Apr 05, 2019 at 04:55:04PM -0700, Matt Mullins wrote:
> From: Andrew Hall <hall@...com>
> 
> This adds four tracepoints to nbd, enabling separate tracing of payload
> and header sending/receipt.
> 
> In the send path for headers that have already been sent, we also
> explicitly initialize the handle so it can be referenced by the later
> tracepoint.
> 
> Signed-off-by: Andrew Hall <hall@...com>
> Signed-off-by: Matt Mullins <mmullins@...com>
> ---
>  drivers/block/nbd.c        |  8 ++++
>  include/trace/events/nbd.h | 92 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 100 insertions(+)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 7393d04d255c..d3d914620f66 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -513,6 +513,10 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
>  	if (sent) {
>  		if (sent >= sizeof(request)) {
>  			skip = sent - sizeof(request);
> +
> +			// initialize handle for tracing purposes
> +			handle = nbd_cmd_handle(cmd);
> +

Don't use c++ style commenting.

>  			goto send_pages;
>  		}
>  		iov_iter_advance(&from, sent);
> @@ -536,6 +540,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
>  		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
>  	result = sock_xmit(nbd, index, 1, &from,
>  			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
> +	trace_nbd_header_sent(req, handle);
>  	if (result <= 0) {
>  		if (was_interrupted(result)) {
>  			/* If we havne't sent anything we can just return BUSY,
> @@ -608,6 +613,7 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
>  		bio = next;
>  	}
>  out:
> +	trace_nbd_payload_sent(req, handle);
>  	nsock->pending = NULL;
>  	nsock->sent = 0;
>  	return 0;
> @@ -655,6 +661,7 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
>  			tag, req);
>  		return ERR_PTR(-ENOENT);
>  	}
> +	trace_nbd_header_received(req, handle);
>  	cmd = blk_mq_rq_to_pdu(req);
>  
>  	mutex_lock(&cmd->lock);
> @@ -708,6 +715,7 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
>  		}
>  	}
>  out:
> +	trace_nbd_payload_received(req, handle);
>  	mutex_unlock(&cmd->lock);
>  	return ret ? ERR_PTR(ret) : cmd;
>  }
> diff --git a/include/trace/events/nbd.h b/include/trace/events/nbd.h
> index 5928255ed02e..eef476fef95a 100644
> --- a/include/trace/events/nbd.h
> +++ b/include/trace/events/nbd.h
> @@ -7,6 +7,98 @@
>  
>  #include <linux/tracepoint.h>
>  
> +TRACE_EVENT(nbd_header_sent,
> +
> +	TP_PROTO(struct request *req, u64 handle),
> +
> +	TP_ARGS(req, handle),
> +
> +	TP_STRUCT__entry(
> +		__field(struct request *, req)
> +		__field(u64, handle)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->req = req;
> +		__entry->handle = handle;
> +	),
> +
> +	TP_printk(
> +		"nbd header sent: request %p, handle 0x%016llx",
> +		__entry->req,
> +		__entry->handle
> +	)
> +);
> +

These are all the same, use DECLARE_EVENT_CLASS() and then just DEFINE_EVENT()
for each individual event.  Also no pointers, we don't want to leak pointers to
userspace for stuff.  Thanks,

Josef