Re: [PATCH 5/8] xfs_scrub: use data/rtdev parallelization estimates for the read-verify pool

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Feb 04, 2019 at 12:35:00PM -0600, Eric Sandeen wrote:
> On 12/19/18 1:30 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Since we use the same read-verify pool object to dispatch file data read
> > requests for both the data device and the realtime device, we should
> > create enough IO threads to handle the estimated parallelization of both
> > devices, not just the data device.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> 
> So if rtdev is on SSD and datadev is on a rotational device, won't we
> possibly still Launch All Threads at the rotational device for this
> case, and won't that still hurt?  I'm not sure it works to lump these
> together, does it?  (I also don't know if it can be done another way...)

Hmm.  I think we /could/ have separate readverify pools for data and rt
devices.  Let me look into that...

--D

> -Eric
> 
> 
> > ---
> >  scrub/phase6.c |   20 ++++++++++++++++++--
> >  1 file changed, 18 insertions(+), 2 deletions(-)
> > 
> > 
> > diff --git a/scrub/phase6.c b/scrub/phase6.c
> > index ead48d77..cbda9b53 100644
> > --- a/scrub/phase6.c
> > +++ b/scrub/phase6.c
> > @@ -435,6 +435,22 @@ xfs_check_rmap(
> >  	return true;
> >  }
> >  
> > +/*
> > + * Estimate the amount of parallelization possible for scanning file data on
> > + * the data and realtime devices.
> > + */
> > +static unsigned int
> > +phase6_threads(
> > +	struct scrub_ctx	*ctx)
> > +{
> > +	unsigned int		nr = disk_heads(ctx->datadev);
> > +
> > +	if (ctx->rtdev)
> > +		nr += disk_heads(ctx->rtdev);
> > +
> > +	return nr > nproc ? nproc : nr;
> > +}
> > +
> >  /*
> >   * Read verify all the file data blocks in a filesystem.  Since XFS doesn't
> >   * do data checksums, we trust that the underlying storage will pass back
> > @@ -469,7 +485,7 @@ xfs_scan_blocks(
> >  	}
> >  
> >  	ve.readverify = read_verify_pool_init(ctx, ctx->geo.blocksize,
> > -			xfs_check_rmap_ioerr, disk_heads(ctx->datadev));
> > +			xfs_check_rmap_ioerr, phase6_threads(ctx));
> >  	if (!ve.readverify) {
> >  		moveon = false;
> >  		str_info(ctx, ctx->mntpoint,
> > @@ -525,7 +541,7 @@ xfs_estimate_verify_work(
> >  		return moveon;
> >  
> >  	*items = ((d_blocks - d_bfree) + (r_blocks - r_bfree)) << ctx->blocklog;
> > -	*nr_threads = disk_heads(ctx->datadev);
> > +	*nr_threads = phase6_threads(ctx);
> >  	*rshift = 20;
> >  	return moveon;
> >  }
> >