linux-kernel - Re: [PATCH] net/9p: Convert net/9p protocol dumps to tracepoints

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Date:	Tue, 09 Aug 2011 19:58:38 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Steven Rostedt <srostedt@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	Pekka Enberg <penberg@...nel.org>,
	v9fs-developer@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] net/9p: Convert net/9p protocol dumps to tracepoints

On Tue, 09 Aug 2011 08:53:15 -0400, Steven Rostedt <srostedt@...hat.com> wrote:
> On Tue, 2011-08-09 at 18:12 +0530, Aneesh Kumar K.V wrote:
> 
> > +#define P9_PROTO_DUMP_SZ (16 * 3 + 2 + 16 + 1)
> 
> Wow, you're making your event have 67 byte arrays, two of them.
> 
> > +TRACE_EVENT(9p_protocol_dump,
> > +	    TP_PROTO(struct p9_client *clnt, struct p9_fcall *pdu),
> > +
> > +	    TP_ARGS(clnt, pdu),
> > +
> > +	    TP_STRUCT__entry(
> > +		    __field(	__u64,		clnt				)
> > +		    __field(	__u8,		type				)
> > +		    __field(	__u16,		tag				)
> > +		    __array(	unsigned char,	line1,	P9_PROTO_DUMP_SZ	)
> > +		    __array(	unsigned char,	line2,	P9_PROTO_DUMP_SZ	)
> > +		    ),
> 
> Wouldn't it be better to put this as two unsigned char arrays of 16
> bytes?
> 
> > +
> > +	    TP_fast_assign(
> > +		    const u8 *ptr   =  pdu->sdata;
> > +		    __entry->clnt   =  (__u64)clnt;
> > +		    __entry->type   =  pdu->id;
> > +		    __entry->tag    =  pdu->tag;
> > +		    hex_dump_to_buffer(ptr, 16, 16,
> > +				       1, __entry->line1, P9_PROTO_DUMP_SZ, true);
> > +		    hex_dump_to_buffer(ptr + 16, 16, 16,
> > +				       1, __entry->line2, P9_PROTO_DUMP_SZ, true);
> > +		    ),
> > +
> > +	    TP_printk("clnt %lu %s(tag = %d)\n%.8x: %s\n%.8x: %s\n",
> > +		      (long)__entry->clnt, show_9p_op(__entry->type),
> > +		      __entry->tag, 0, __entry->line1, 16 , __entry->line2)
> 
> Yeah, you would need to make the above ugly to print out the array, but
> it's not that hard. And you will be saving 102 bytes per event in the
> ring buffer, which is very expensive real-estate. Not to mention the
> time it takes to copy all that.
> 

Any suggestion on how to get this pretty printing of the hex data. I can
update print_hex_dump_bytes to dump the hex data to a buffer. But not
sure where i can free the buffer after using that in TP_printk. 

-aneesh
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