linux-kernel - Re: [PATCHv2 1/4] nvme: trace nvme queue identifiers

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Date:   Fri, 29 Jun 2018 09:57:29 +0200
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Johannes Thumshirn <jthumshirn@...e.de>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 1/4] nvme: trace nvme queue identifiers

On Thu, Jun 28, 2018 at 03:49:53PM -0600, Keith Busch wrote:
> We can not match a command to its completion based on the command id
> alone. We need the submitting queue identifier to pair the completion,
> so this patch adds that to the trace buffer.
> 
> This patch is also collapsing the admin and io submission traces into
> a single one since we don't need to duplicate this and creating
> unnecessary code branches.
> 
> Signed-off-by: Keith Busch <keith.busch@...el.com>
> ---
>  drivers/nvme/host/core.c  |  7 +++----
>  drivers/nvme/host/trace.h | 41 ++++++++++-------------------------------
>  2 files changed, 13 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 46df030b2c3f..398a5fb26603 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -97,6 +97,8 @@ static dev_t nvme_chr_devt;
>  static struct class *nvme_class;
>  static struct class *nvme_subsys_class;
>  
> +static void nvme_remove_invalid_namespaces(struct nvme_ctrl *ctrl,
> +					   unsigned nsid);

Huh?

>  static void nvme_ns_remove(struct nvme_ns *ns);
>  static int nvme_revalidate_disk(struct gendisk *disk);
>  static void nvme_put_subsystem(struct nvme_subsystem *subsys);
> @@ -652,10 +654,7 @@ blk_status_t nvme_setup_cmd(struct nvme_ns *ns, struct request *req,
>  	}
>  
>  	cmd->common.command_id = req->tag;
> -	if (ns)
> -		trace_nvme_setup_nvm_cmd(req->q->id, cmd);
> -	else
> -		trace_nvme_setup_admin_cmd(cmd);
> +	trace_nvme_setup_nvm_cmd(req, cmd);
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(nvme_setup_cmd);
> diff --git a/drivers/nvme/host/trace.h b/drivers/nvme/host/trace.h
> index 01390f0e1671..42c99445dd96 100644
> --- a/drivers/nvme/host/trace.h
> +++ b/drivers/nvme/host/trace.h
> @@ -75,34 +75,9 @@ const char *nvme_trace_parse_nvm_cmd(struct trace_seq *p, u8 opcode,
>  #define __parse_nvme_cmd(opcode, cdw10) \
>  	nvme_trace_parse_nvm_cmd(p, opcode, cdw10)
>  
> -TRACE_EVENT(nvme_setup_admin_cmd,
> -	    TP_PROTO(struct nvme_command *cmd),
> -	    TP_ARGS(cmd),
> -	    TP_STRUCT__entry(
> -		    __field(u8, opcode)
> -		    __field(u8, flags)
> -		    __field(u16, cid)
> -		    __field(u64, metadata)
> -		    __array(u8, cdw10, 24)
> -	    ),
> -	    TP_fast_assign(
> -		    __entry->opcode = cmd->common.opcode;
> -		    __entry->flags = cmd->common.flags;
> -		    __entry->cid = cmd->common.command_id;
> -		    __entry->metadata = le64_to_cpu(cmd->common.metadata);
> -		    memcpy(__entry->cdw10, cmd->common.cdw10,
> -			   sizeof(__entry->cdw10));
> -	    ),
> -	    TP_printk(" cmdid=%u, flags=0x%x, meta=0x%llx, cmd=(%s %s)",
> -		      __entry->cid, __entry->flags, __entry->metadata,
> -		      show_admin_opcode_name(__entry->opcode),
> -		      __parse_nvme_admin_cmd(__entry->opcode, __entry->cdw10))
> -);
> -
> -
>  TRACE_EVENT(nvme_setup_nvm_cmd,
> -	    TP_PROTO(int qid, struct nvme_command *cmd),
> -	    TP_ARGS(qid, cmd),
> +	    TP_PROTO(struct request *req, struct nvme_command *cmd),
> +	    TP_ARGS(req, cmd),
>  	    TP_STRUCT__entry(
>  		    __field(int, qid)
>  		    __field(u8, opcode)
> @@ -113,7 +88,7 @@ TRACE_EVENT(nvme_setup_nvm_cmd,
>  		    __array(u8, cdw10, 24)
>  	    ),
>  	    TP_fast_assign(
> -		    __entry->qid = qid;
> +		    __entry->qid = blk_mq_unique_tag_to_hwq(blk_mq_unique_tag(req)) + !!req->rq_disk;

This looks pretty ugly.  I'd much prefer:

		if (req->rq_disk)
			__entry->qid = blk_mq_unique_tag_to_hwq(blk_mq_unique_tag(req));
		else
			__entry->qid = 0;

Also the indentation in the existing code seems weird and not based
on tabs.  We should fix that up.
	
> +		      __entry->qid ?
> +				show_opcode_name(__entry->opcode) :
> +				show_admin_opcode_name(__entry->opcode),
> +		      __entry->qid ?
> +				__parse_nvme_cmd(__entry->opcode, __entry->cdw10) :
> +				__parse_nvme_admin_cmd(__entry->opcode, __entry->cdw10))
>  );

Can we hide this?  E.g. pass the qid to show_opcode_name and then
implement show_opcode_name as:

#define show_opcode_name(qid, opcode) \
	(qid ? show_admin_opcode_name(opcode) : show_nvm_opcode_name(opcode))

Same for __parse_nvme_cmd.

> +		    __entry->qid = blk_mq_unique_tag_to_hwq(blk_mq_unique_tag(req)) + !!req->rq_disk;

Same as above.

In fact I guess we should just have a helper:

static inline u16 nvme_req_to_qid(struct request *req)
{
	if (!req->rq_disk)
		return 0;
	return blk_mq_unique_tag_to_hwq(blk_mq_unique_tag(req));
}