linux-kernel - Re: [PATCH][v2] blktrace: conversion to tracepoints

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Date:	Wed, 29 Oct 2008 13:50:56 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][v2] blktrace: conversion to tracepoints

Em Wed, Oct 29, 2008 at 02:18:55PM +0100, Jens Axboe escreveu:
> On Wed, Oct 29 2008, Arnaldo Carvalho de Melo wrote:
> > Hi Jens,
> > 
> > 	Now that the tracepoints infrastructure is merged I updated the
> > patch, please take a look.
> > 
> > 	One suggestion I got was to have things like:
> > 
> >   trace_block_unplug_io(q, q->rq.count[READ] + q->rq.count[WRITE]);
> > 
> > 	That was:
> > 
> >   blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL,
> > 	                q->rq.count[READ] + q->rq.count[WRITE]);
> > 
> > 	To be:
> > 
> >   trace_block_unplug_io(q, q->rq.count[READ], q->rq.count[WRITE]);
> > 
> > 	Or even:
> > 
> >   trace_block_unplug_io(q);
> > 
> > 	And on  blk_add_trace_unplug_io tracepoint do the math and feed
> > it to __blk_add_trace.
> > 
> >         So that the information on the number of types of requests
> > instead of the sum, what do you think? Overengineering? For blktrace it
> > would end up being preserved as is in, say:
> > 
> > static void blk_add_trace_unplug_io(struct request_queue *q,
> > 				    unsigned int rd, unsigned int wr)
> > {
> >         struct blk_trace *bt = q->blk_trace;
> > 
> >         if (bt) {
> >                 __be64 rpdu = cpu_to_be64(rd + wr);
> > 
> >                 __blk_add_trace(bt, 0, 0, 0, BLK_TA_UNPLUG_IO, 0,
> >                                 sizeof(rpdu), &rpdu);
> >         }
> > }
> > 
> > 	Perhaps doing it as 'trace_block_unplug_io(q)' would be the best
> > scenario, as the tracepoint user can look at struct_request queue at
> > will anyway and the code gets cleaner :-)
> > 
> > 	Feel free to point any disgusting aspect, perhaps there is at
> > least one to warn me about fixing 8-)
> 
> You my as well pass the members separately now that it's a specific call
> anyway, to avoid doing the calculation when tracing is disabled.
> 
> Patch looks straight forward. Perhaps it would be cleaner to use an
> atomic type for the reference?

I'll do that now and repost, thanks,

- Arnaldo
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