svn commit: r269814 - head/sys/dev/xen/blkfront

[John-Mark Gurney]

Alexander Motin wrote this message on Thu, Aug 28, 2014 at 21:23 +0300:
> Hi, Roger.
> 
> It looks to me like this commit does not work as it should. I got
> problem when I just tried `newfs /dev/ada0 ; mount /dev/ada0 /mnt`.
> Somehow newfs does not produce valid filesystem. Problem is reliably
> repeatable and reverting this commit fixes it.
> 
> I found at least one possible cause there: If original data buffer is
> unmapped, misaligned and not physically contiguous, then present x86
> bus_dmamap_load_bio() implementation will process each physically
> contiguous segment separately. Due to the misalignment first and last
> physical segments may have size not multiple to 512 bytes. Since each
> segment processed separately, they are not joined together, and
> xbd_queue_cb() is getting segments not multiple to 512 bytes. Attempt to
> convert them to exact number of sectors in the driver cause data corruption.

Are you sure this isn't a problem w/ the tag not properly specifying
the correct alignement?  Also, I don't think there is a way for busdma
to say that you MUST have a segment be a multiple of 512, though you
could use a 512 boundary, but that would force all segments to only be
512 bytes...

> This is a bug of the busdma code, and until it is fixed I don't see
> solution other then temporary reverting this commit.
> 
> On 11.08.2014 18:37, Roger Pau Monné   wrote:
> > Author: royger
> > Date: Mon Aug 11 15:37:02 2014
> > New Revision: 269814
> > URL: http://svnweb.freebsd.org/changeset/base/269814
> > 
> > Log:
> >   blkfront: add support for unmapped IO
> >   
> >   Using unmapped IO is really beneficial when running inside of a VM,
> >   since it avoids IPIs to other vCPUs in order to invalidate the
> >   mappings.
> >   
> >   This patch adds unmapped IO support to blkfront. The following tests
> >   results have been obtained when running on a Xen host without HAP:
> >   
> >   PVHVM
> >        3165.84 real      6354.17 user      4483.32 sys
> >   PVHVM with unmapped IO
> >        2099.46 real      4624.52 user      2967.38 sys
> >   
> >   This is because when running using shadow page tables TLB flushes and
> >   range invalidations are much more expensive, so using unmapped IO
> >   provides a very important performance boost.
> >   
> >   Sponsored by:	Citrix Systems R&D
> >   Tested by:	robak
> >   MFC after:	1 week
> >   PR:		191173
> >   
> >   dev/xen/blkfront/blkfront.c:
> >    - Add and announce support for unmapped IO.
> > 
> > Modified:
> >   head/sys/dev/xen/blkfront/blkfront.c
> > 
> > Modified: head/sys/dev/xen/blkfront/blkfront.c
> > ==============================================================================
> > --- head/sys/dev/xen/blkfront/blkfront.c	Mon Aug 11 15:06:07 2014	(r269813)
> > +++ head/sys/dev/xen/blkfront/blkfront.c	Mon Aug 11 15:37:02 2014	(r269814)
> > @@ -272,8 +272,12 @@ xbd_queue_request(struct xbd_softc *sc, 
> >  {
> >  	int error;
> >  
> > -	error = bus_dmamap_load(sc->xbd_io_dmat, cm->cm_map, cm->cm_data,
> > -	    cm->cm_datalen, xbd_queue_cb, cm, 0);
> > +	if (cm->cm_bp != NULL)
> > +		error = bus_dmamap_load_bio(sc->xbd_io_dmat, cm->cm_map,
> > +		    cm->cm_bp, xbd_queue_cb, cm, 0);
> > +	else
> > +		error = bus_dmamap_load(sc->xbd_io_dmat, cm->cm_map,
> > +		    cm->cm_data, cm->cm_datalen, xbd_queue_cb, cm, 0);
> >  	if (error == EINPROGRESS) {
> >  		/*
> >  		 * Maintain queuing order by freezing the queue.  The next
> > @@ -333,8 +337,6 @@ xbd_bio_command(struct xbd_softc *sc)
> >  	}
> >  
> >  	cm->cm_bp = bp;
> > -	cm->cm_data = bp->bio_data;
> > -	cm->cm_datalen = bp->bio_bcount;
> >  	cm->cm_sector_number = (blkif_sector_t)bp->bio_pblkno;
> >  
> >  	switch (bp->bio_cmd) {
> > @@ -993,7 +995,7 @@ xbd_instance_create(struct xbd_softc *sc
> >  
> >  	sc->xbd_disk->d_mediasize = sectors * sector_size;
> >  	sc->xbd_disk->d_maxsize = sc->xbd_max_request_size;
> > -	sc->xbd_disk->d_flags = 0;
> > +	sc->xbd_disk->d_flags = DISKFLAG_UNMAPPED_BIO;
> >  	if ((sc->xbd_flags & (XBDF_FLUSH|XBDF_BARRIER)) != 0) {
> >  		sc->xbd_disk->d_flags |= DISKFLAG_CANFLUSHCACHE;
> >  		device_printf(sc->xbd_dev,

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."