From: Christoph Hellwig on
On Tue, Apr 20, 2010 at 12:41:51PM +1000, Dave Chinner wrote:
> From: From: Jens Axboe <jens.axboe(a)oracle.com>
>
> Trace queue/sched/exec parts of the writeback loop.

If you move the CREATE_TRACE_POINTS into fs-writeback.c and include
<trace/events/writeback.h> after the sturcture defintions there's no
need to move them to a header.

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From: Christoph Hellwig on
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/writeback.h>

It might be worth to add a comment why this is in an unusal place.

Otherwise looks good,


Reviewed-by: Christoph Hellwig <hch(a)lst.de>
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From: Andrew Morton on
On Tue, 25 May 2010 20:54:07 +1000
Dave Chinner <david(a)fromorbit.com> wrote:

> From: From: Jens Axboe <jens.axboe(a)oracle.com>
>
> Trace queue/sched/exec parts of the writeback loop.

It would be most useful if this patchset's description provided sample
tracing output, so we can see what the patch is actually providing us.

> -#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
> -
> -/*
> - * We don't actually have pdflush, but this one is exported though /proc...
> - */
> -int nr_pdflush_threads;
> -
> /*
> * Passed into wb_writeback(), essentially a subset of writeback_control
> */
> @@ -63,6 +57,16 @@ struct bdi_work {
> unsigned long state; /* flag bits, see WS_* */
> };
>
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/writeback.h>
> +
> +#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)

Could/should be implemented in C.

> +/*
> + * We don't actually have pdflush, but this one is exported though /proc...
> + */
> +int nr_pdflush_threads;

So this is always zero now?

We don't want to keep it forever. Add a
printk_once("nr_pdflush_threads is deprecated") when someone reads it,
remove it in 2014.

>
> ...
>
> --- /dev/null
> +++ b/include/trace/events/writeback.h
> @@ -0,0 +1,171 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM writeback
> +
> +#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)

Seems wrong. If you define TRACE_HEADER_MULTI_READ then include this
header twice, things explode. Which negates the purpose of
_TRACE_WRITEBACK_H.

> +#define _TRACE_WRITEBACK_H
> +
> +#include <linux/backing-dev.h>
> +#include <linux/writeback.h>
> +
> +TRACE_EVENT(writeback_queue,
> +
> + TP_PROTO(struct backing_dev_info *bdi, struct wb_writeback_args *args),
> +
> + TP_ARGS(bdi, args),
> +
> + TP_STRUCT__entry(
> + __array(char, name, 16)
> + __field(long, nr_pages)
> + __field(int, sb)
> + __field(int, sync_mode)
> + __field(int, for_kupdate)
> + __field(int, range_cyclic)
> + __field(int, for_background)
> + ),
> +
> + TP_fast_assign(
> + strncpy(__entry->name, dev_name(bdi->dev), 16);
> + __entry->nr_pages = args->nr_pages;
> + __entry->sb = !!args->sb;
> + __entry->for_kupdate = args->for_kupdate;
> + __entry->range_cyclic = args->range_cyclic;
> + __entry->for_background = args->for_background;
> + ),
> +
> + TP_printk("%s: pages=%ld, sb=%d, kupdate=%d, range_cyclic=%d "
> + "for_background=%d", __entry->name, __entry->nr_pages,
> + __entry->sb, __entry->for_kupdate,
> + __entry->range_cyclic, __entry->for_background)
> +);
> +

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From: Dave Chinner on
On Thu, May 27, 2010 at 02:32:33PM -0700, Andrew Morton wrote:
> On Tue, 25 May 2010 20:54:07 +1000
> Dave Chinner <david(a)fromorbit.com> wrote:
>
> > From: From: Jens Axboe <jens.axboe(a)oracle.com>
> >
> > Trace queue/sched/exec parts of the writeback loop.
>
> It would be most useful if this patchset's description provided sample
> tracing output, so we can see what the patch is actually providing us.

This is just a forward port of Jen's patch. I guess I'll have to
clean it up some more...

>
> > -#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
> > -
> > -/*
> > - * We don't actually have pdflush, but this one is exported though /proc...
> > - */
> > -int nr_pdflush_threads;
> > -
> > /*
> > * Passed into wb_writeback(), essentially a subset of writeback_control
> > */
> > @@ -63,6 +57,16 @@ struct bdi_work {
> > unsigned long state; /* flag bits, see WS_* */
> > };
> >
> > +#define CREATE_TRACE_POINTS
> > +#include <trace/events/writeback.h>
> > +
> > +#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
>
> Could/should be implemented in C.

OK.

>
> > +/*
> > + * We don't actually have pdflush, but this one is exported though /proc...
> > + */
> > +int nr_pdflush_threads;
>
> So this is always zero now?

I guess so. I'd forgotten that this was in the original patch....

> We don't want to keep it forever. Add a
> printk_once("nr_pdflush_threads is deprecated") when someone reads it,
> remove it in 2014.

OK.

> > --- /dev/null
> > +++ b/include/trace/events/writeback.h
> > @@ -0,0 +1,171 @@
> > +#undef TRACE_SYSTEM
> > +#define TRACE_SYSTEM writeback
> > +
> > +#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)
>
> Seems wrong. If you define TRACE_HEADER_MULTI_READ then include this
> header twice, things explode. Which negates the purpose of
> _TRACE_WRITEBACK_H.

Every other trace event header does this, so if it's wrong then the
same mistake is in at least 30 files now. I don't know enough about
the tracing code to know why this is done, and I'm not keen to
address such a mistake here...

Cheers,

Dave.
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Dave Chinner
david(a)fromorbit.com
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From: Steven Rostedt on
On Thu, 2010-05-27 at 14:32 -0700, Andrew Morton wrote:

> > --- /dev/null
> > +++ b/include/trace/events/writeback.h
> > @@ -0,0 +1,171 @@
> > +#undef TRACE_SYSTEM
> > +#define TRACE_SYSTEM writeback
> > +
> > +#if !defined(_TRACE_WRITEBACK_H) || defined(TRACE_HEADER_MULTI_READ)
>
> Seems wrong. If you define TRACE_HEADER_MULTI_READ then include this
> header twice, things explode. Which negates the purpose of
> _TRACE_WRITEBACK_H.

That's intended. It is documented in
samples/trace_events/trace-events-samples.h

The purpose of the TRACE_HEADER_MULTI_READ is to read the trace header
multi times. ;-)


You can also read about it here:

http://lwn.net/Articles/379903/

here:

http://lwn.net/Articles/381064/

and here:

http://lwn.net/Articles/383362/

-- Steve

>
> > +#define _TRACE_WRITEBACK_H
> > +
> > +#include <linux/backing-dev.h>
> > +#include <linux/writeback.h>
> > +

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