On Tue, Jan 04, 2011 at 05:02:40AM -0500, Christoph Hellwig wrote:
> > This patch uses 32-way threading which results in no noticable
> > slowdown on single SATA drives with NCQ, but results in ~10x
> > reduction in runtime on a 12 disk RAID-0 array.
>
> Shouldn't we have at least an option to allow tuning this value,
> similar to the ag_stride? In fact I wonder why phase 3/4 should
> use different values for it than phase2.
Phase 3/4/5 use agressive prefetch to try to maximise throughput,
while phase 2 has no prefetch and uses synchronous reads.
Effectively the use of lots of parallelism simply keeps multiple IOs
in flight rather than reading them one at a time, hence reducing the
effective IO latency.
>
> > @@ -75,8 +80,10 @@ scan_sbtree(
> > xfs_agblock_t bno,
> > xfs_agnumber_t agno,
> > int suspect,
> > - int isroot),
> > - int isroot)
> > + int isroot,
> > + struct aghdr_cnts *agcnts),
> > + int isroot,
> > + struct aghdr_cnts *agcnts)
>
> Please make this a
>
> void *priv
>
> to keep scan_sbtree generic.
OK.
> > * Scan an AG for obvious corruption.
> > *
> > * Note: This code is not reentrant due to the use of global variables.
>
> That's not true any more I think.
Good point.
> > +#define SCAN_THREADS 32
> > +
> > +void
> > +scan_ags(
> > + struct xfs_mount *mp)
> > +{
> > + struct aghdr_cnts agcnts[mp->m_sb.sb_agcount];
> > + pthread_t thr[SCAN_THREADS];
> > + __uint64_t fdblocks = 0;
> > + __uint64_t icount = 0;
> > + __uint64_t ifreecount = 0;
> > + int i, j, err;
> > +
> > + /*
> > + * scan a few AGs in parallel. The scan is IO latency bound,
> > + * so running a few at a time will speed it up significantly.
> > + */
> > + for (i = 0; i < mp->m_sb.sb_agcount; i += SCAN_THREADS) {
>
> I think this should use the workqueues from repair/threads.c. Just
> create a workqueue with 32 threads, and then enqueue all the AGs.
Ok. I just used an API I'm familiar with and didn't have to think
about.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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