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    SubjectRe: [PATCH 1/6] writeback: initial tracing support
    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@fromorbit.com> wrote:
    >
    > > From: From: Jens Axboe <jens.axboe@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.
    --
    Dave Chinner
    david@fromorbit.com


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