svn commit: r244793 - in user/attilio/membarclean/dev: drm drm2 netmap virtio
Attilio Rao
attilio at freebsd.org
Fri Dec 28 22:58:53 UTC 2012
On Fri, Dec 28, 2012 at 10:43 PM, Bryan Venteicher
<bryan.venteicher at gmail.com> wrote:
> On Fri, Dec 28, 2012 at 4:18 PM, Attilio Rao <attilio at 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).
I think you are referring to the wmb() usage.
However, right now we don't guarantee _8 and _16 atomic ops on every
architecture and we should stay that way. This means that even if you
introduce the _16 variant for all the architecture this is not enough
to yet use it in virtio.
I have a couple of ideas on how to fix the wmb() one, I will send you
an e-mail when I get to it.
Attilio
--
Peace can only be achieved by understanding - A. Einstein
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