Date: Thu, 28 Aug 2014 11:45:15 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: Alexander Motin <mav@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Roger Pau =?iso-8859-1?Q?Monn=E9?= <royger@freebsd.org>, src-committers@freebsd.org Subject: Re: svn commit: r269814 - head/sys/dev/xen/blkfront Message-ID: <20140828184515.GV71691@funkthat.com> In-Reply-To: <53FF7386.3050804@FreeBSD.org> References: <53e8e31e.2179.30c1c657@svn.freebsd.org> <53FF7386.3050804@FreeBSD.org>
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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."
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