Date: Fri, 28 Dec 2012 16:43:19 -0600 From: Bryan Venteicher <bryan.venteicher@gmail.com> To: Attilio Rao <attilio@freebsd.org> Cc: src-committers@freebsd.org, svn-src-user@freebsd.org Subject: Re: svn commit: r244793 - in user/attilio/membarclean/dev: drm drm2 netmap virtio Message-ID: <CAGaYwLcJ0S=AmqPZoBS_ZzwrKVJZEpmGyq0yJm5H-kW01susZQ@mail.gmail.com> In-Reply-To: <201212282218.qBSMIfX2015054@svn.freebsd.org> References: <201212282218.qBSMIfX2015054@svn.freebsd.org>
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On Fri, Dec 28, 2012 at 4:18 PM, Attilio Rao <attilio@freebsd.org> wrote: > Author: attilio > Date: Fri Dec 28 22:18:41 2012 > New Revision: 244793 > URL: http://svnweb.freebsd.org/changeset/base/244793 > > Log: > - Remove rmb() usage from netmap and replace it with intended operation > to do actual memory fetching reads. > - GC unused DRM_WRITEMEMORYBARRIER() from drm and drm2. > - Use atomic_load_acq_*() in virtio and drm2 in places that don't need > to use rmb(). > > All these changes remove completely rmb() from MI code, with the > exception of cxgbe which will be hammered in a followup commit. > > Modified: > user/attilio/membarclean/dev/drm/drmP.h > user/attilio/membarclean/dev/drm2/drmP.h > user/attilio/membarclean/dev/drm2/drm_atomic.h > user/attilio/membarclean/dev/drm2/drm_irq.c > user/attilio/membarclean/dev/netmap/netmap.c > user/attilio/membarclean/dev/virtio/virtqueue.c > > Modified: user/attilio/membarclean/dev/drm/drmP.h > ============================================================================== > --- user/attilio/membarclean/dev/drm/drmP.h Fri Dec 28 22:06:50 2012 (r244792) > +++ user/attilio/membarclean/dev/drm/drmP.h Fri Dec 28 22:18:41 2012 (r244793) > @@ -241,11 +241,9 @@ typedef u_int32_t u32; > typedef u_int16_t u16; > typedef u_int8_t u8; > > -/* DRM_READMEMORYBARRIER() prevents reordering of reads. > - * DRM_WRITEMEMORYBARRIER() prevents reordering of writes. > +/* DRM_WRITEMEMORYBARRIER() prevents reordering of writes. > * DRM_MEMORYBARRIER() prevents reordering of reads and writes. > */ > -#define DRM_READMEMORYBARRIER() rmb() > #define DRM_WRITEMEMORYBARRIER() wmb() > #define DRM_MEMORYBARRIER() mb() > > > Modified: user/attilio/membarclean/dev/drm2/drmP.h > ============================================================================== > --- user/attilio/membarclean/dev/drm2/drmP.h Fri Dec 28 22:06:50 2012 (r244792) > +++ user/attilio/membarclean/dev/drm2/drmP.h Fri Dec 28 22:18:41 2012 (r244793) > @@ -263,11 +263,9 @@ typedef int32_t s32; > typedef int16_t s16; > typedef int8_t s8; > > -/* DRM_READMEMORYBARRIER() prevents reordering of reads. > - * DRM_WRITEMEMORYBARRIER() prevents reordering of writes. > +/* DRM_WRITEMEMORYBARRIER() prevents reordering of writes. > * DRM_MEMORYBARRIER() prevents reordering of reads and writes. > */ > -#define DRM_READMEMORYBARRIER() rmb() > #define DRM_WRITEMEMORYBARRIER() wmb() > #define DRM_MEMORYBARRIER() mb() > > > Modified: user/attilio/membarclean/dev/drm2/drm_atomic.h > ============================================================================== > --- user/attilio/membarclean/dev/drm2/drm_atomic.h Fri Dec 28 22:06:50 2012 (r244792) > +++ user/attilio/membarclean/dev/drm2/drm_atomic.h Fri Dec 28 22:18:41 2012 (r244793) > @@ -38,6 +38,7 @@ typedef u_int32_t atomic_t; > > #define atomic_set(p, v) (*(p) = (v)) > #define atomic_read(p) (*(p)) > +#define atomic_read_acq(p) atomic_load_acq_int(p) > #define atomic_inc(p) atomic_add_int(p, 1) > #define atomic_dec(p) atomic_subtract_int(p, 1) > #define atomic_add(n, p) atomic_add_int(p, n) > > Modified: user/attilio/membarclean/dev/drm2/drm_irq.c > ============================================================================== > --- user/attilio/membarclean/dev/drm2/drm_irq.c Fri Dec 28 22:06:50 2012 (r244792) > +++ user/attilio/membarclean/dev/drm2/drm_irq.c Fri Dec 28 22:18:41 2012 (r244793) > @@ -701,8 +701,7 @@ u32 drm_vblank_count_and_time(struct drm > do { > cur_vblank = atomic_read(&dev->_vblank_count[crtc]); > *vblanktime = vblanktimestamp(dev, crtc, cur_vblank); > - rmb(); > - } while (cur_vblank != atomic_read(&dev->_vblank_count[crtc])); > + } while (cur_vblank != atomic_read_acq(&dev->_vblank_count[crtc])); > > return cur_vblank; > } > > Modified: user/attilio/membarclean/dev/netmap/netmap.c > ============================================================================== > --- user/attilio/membarclean/dev/netmap/netmap.c Fri Dec 28 22:06:50 2012 (r244792) > +++ user/attilio/membarclean/dev/netmap/netmap.c Fri Dec 28 22:18:41 2012 (r244793) > @@ -98,6 +98,9 @@ MALLOC_DEFINE(M_NETMAP, "netmap", "Netwo > #include <net/netmap.h> > #include <dev/netmap/netmap_kern.h> > > +#define MEMFETCH(var) \ > + (__DEVOLATILE(__typeof(var), *((volatile __typeof(var) *)&var))) > + > u_int netmap_total_buffers; > u_int netmap_buf_size; > char *netmap_buffer_base; /* address of an invalid buffer */ > @@ -1081,10 +1084,7 @@ error: > error = ENXIO; > break; > } > - rmb(); /* make sure following reads are not from cache */ > - > - > - ifp = priv->np_ifp; /* we have a reference */ > + ifp = MEMFETCH(priv->np_ifp); > > if (ifp == NULL) { > D("Internal error: nifp != NULL && ifp == NULL"); > @@ -1194,9 +1194,7 @@ netmap_poll(struct cdev *dev, int events > D("No if registered"); > return POLLERR; > } > - rmb(); /* make sure following reads are not from cache */ > - > - ifp = priv->np_ifp; > + ifp = MEMFETCH(priv->np_ifp); > // XXX check for deleting() ? > if ( (ifp->if_capenable & IFCAP_NETMAP) == 0) > return POLLERR; > > Modified: user/attilio/membarclean/dev/virtio/virtqueue.c > ============================================================================== > --- user/attilio/membarclean/dev/virtio/virtqueue.c Fri Dec 28 22:06:50 2012 (r244792) > +++ user/attilio/membarclean/dev/virtio/virtqueue.c Fri Dec 28 22:18:41 2012 (r244793) > @@ -525,8 +525,7 @@ virtqueue_dequeue(struct virtqueue *vq, > used_idx = vq->vq_used_cons_idx++ & (vq->vq_nentries - 1); > uep = &vq->vq_ring.used->ring[used_idx]; > > - rmb(); > - desc_idx = (uint16_t) uep->id; > + desc_idx = (uint16_t)atomic_load_acq_32(&uep->id); > if (len != NULL) > *len = uep->len; > VirtIO uses 16-bit fields which makes it hard to adapt to MI atomic(9). The field here happens to be 32-bits, but that is for alignment purposes. I have a patch from a couple months back that switches VirtIO to atomic_*(), but the mb()'s are still #ifdef in there for the eventual support of arch's without 16-bit atomic(9) (and the patch needs a bit of followup work).
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