Re: [PATCH 05/10] repair: factor out threading setup code

Dave Chinner
2014-02-24T23:19:04Z

On Mon, Feb 24, 2014 at 03:43:05PM -0500, Brian Foster wrote:
> On Mon, Feb 24, 2014 at 05:29:24PM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > The same code is repeated in different places to set up
> > multithreaded prefetching. This can all be factored into a single
> > implementation.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
....
> > static void
> > traverse_ags(
> > - xfs_mount_t *mp)
> > + struct xfs_mount *mp)
> > {
> > - int i;
> > - work_queue_t queue;
> > - prefetch_args_t *pf_args[2];
> > -
> > - /*
> > - * we always do prefetch for phase 6 as it will fill in the gaps
> > - * not read during phase 3 prefetch.
> > - */
> > - queue.mp = mp;
> > - pf_args[0] = start_inode_prefetch(0, 1, NULL);
> > - for (i = 0; i < glob_agcount; i++) {
> > - pf_args[(~i) & 1] = start_inode_prefetch(i + 1, 1,
> > - pf_args[i & 1]);
> > - traverse_function(&queue, i, pf_args[i & 1]);
> > - }
> > + do_inode_prefetch(mp, 0, traverse_function, true, true);
>
> The cover letter indicates the parallelization of phase 6 was dropped,
> but this appears to (conditionally) enable it.

No, it enables prefetch, it does not enable threading. The second
parameter is "0" which means that do_inode_prefetch() executes the
single threaded prefetch walk like the above code. i.e.:

> > + */
> > +void
> > +do_inode_prefetch(
> > + struct xfs_mount *mp,
> > + int stride,

stride = 0

> > + void (*func)(struct work_queue *,
> > + xfs_agnumber_t, void *),
> > + bool check_cache,
> > + bool dirs_only)
> > +{
> > + int i, j;
> > + xfs_agnumber_t agno;
> > + struct work_queue queue;
> > + struct work_queue *queues;
> > + struct prefetch_args *pf_args[2];
> > +
> > + /*
> > + * If the previous phases of repair have not overflowed the buffer
> > + * cache, then we don't need to re-read any of the metadata in the
> > + * filesystem - it's all in the cache. In that case, run a thread per
> > + * CPU to maximise parallelism of the queue to be processed.
> > + */
> > + if (check_cache && !libxfs_bcache_overflowed()) {
> > + queue.mp = mp;
> > + create_work_queue(&queue, mp, libxfs_nproc());
> > + for (i = 0; i < mp->m_sb.sb_agcount; i++)
> > + queue_work(&queue, func, i, NULL);
> > + destroy_work_queue(&queue);
> > + return;
> > + }
> > +
> > + /*
> > + * single threaded behaviour - single prefetch thread, processed
> > + * directly after each AG is queued.
> > + */
> > + if (!stride) {
> > + queue.mp = mp;
> > + pf_args[0] = start_inode_prefetch(0, dirs_only, NULL);
> > + for (i = 0; i < mp->m_sb.sb_agcount; i++) {
> > + pf_args[(~i) & 1] = start_inode_prefetch(i + 1,
> > + dirs_only, pf_args[i & 1]);
> > + func(&queue, i, pf_args[i & 1]);
> > + }
> > + return;
> > + }

So we run this "!stride" code. Hmmmm - maybe you are commenting on
the "check_cache" code? I probably should prevent that from
triggering, too.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com