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

Brian Foster
2014-02-24T23:30:33Z

On Tue, Feb 25, 2014 at 10:16:20AM +1100, Dave Chinner wrote:
> 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.
>

Sorry, I could have been more clear on that. Yes, I'm referring
specifically to setting check_cache to true.

Brian

> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com