Re: [PATCH][v2] blktrace: conversion to tracepoints

Jens Axboe
2008-10-29T13:29:36Z

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?

> @@ -237,6 +243,10 @@ static void blk_trace_cleanup(struct blk_trace *bt)
> free_percpu(bt->sequence);
> free_percpu(bt->msg_data);
> kfree(bt);
> + mutex_lock(&blk_probe_mutex);
> + if (--blk_probes_ref == 0)
> + blk_unregister_tracepoints();
> + mutex_unlock(&blk_probe_mutex);
> }

Then this would be

if (atomic_dec_and_test(&blk_probes_ref))
blk_unregister_tracepoints();

> int blk_trace_remove(struct request_queue *q)
> @@ -428,6 +438,14 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> bt->pid = buts->pid;
> bt->trace_state = Blktrace_setup;
>
> + mutex_lock(&blk_probe_mutex);
> + if (!blk_probes_ref++) {
> + ret = blk_register_tracepoints();
> + if (ret)
> + goto probe_err;
> + }
> + mutex_unlock(&blk_probe_mutex);
> +

And this would be

if (atomic_add_return(&blk_probes_ref, 1) == 1) {
ret = blk_register_tracepoints();
if (ret)
goto probe_err;
}

--
Jens Axboe