Michael S. Tsirkin
2011-Jun-01 10:25 UTC
[PATCHv3] virtio-spec: 64 bit features, used/avail event, fixes
Add an option to modify the notificatin
hand-off in virtio to be basically like Xen:
each side published an index, the other side only triggers
an event when it crosses that index value
(Xen event indexes start at 1, ours start at 0 for
backward-compatiblity, but that's minor).
Since we've run out of bits in the 32 bit field,
I added another 32 bit and bit 31 enables that.
I started with using both flags and indexes in parallel,
but switched to doing either-or: this means we do
not need to tweak memory access ordering as index access just
replaces flags access.
A note on naming: the index replacing avail->flags is named
used_event, the index replacing used->flags is named
avail_event to stress the fact that these actually
point into the other side of the ring:
event is triggered when avail->idx == used->avail_event + 1
and when used->idx == avail->used_event + 1, respectively.
I also documented some more the ordering rules wrt flags/event index
field update.
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
I switched to fedora 15 so a new lyx - hope it's not a problem.
Sorry, no PDF as lyx 2.0 seems to have trouble producing them for me.
virtio-spec.lyx | 756 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 729 insertions(+), 27 deletions(-)
diff --git a/virtio-spec.lyx b/virtio-spec.lyx
index f7c9c38..4f460ce 100644
--- a/virtio-spec.lyx
+++ b/virtio-spec.lyx
@@ -1,21 +1,29 @@
-#LyX 1.6.7 created this file. For more info see http://www.lyx.org/
-\lyxformat 345
+#LyX 2.0 created this file. For more info see http://www.lyx.org/
+\lyxformat 413
\begin_document
\begin_header
\textclass report
\use_default_options false
+\maintain_unincluded_children false
\language english
+\language_package default
\inputencoding auto
+\fontencoding global
\font_roman default
\font_sans default
\font_typewriter default
\font_default_family default
+\use_non_tex_fonts false
\font_sc false
\font_osf false
\font_sf_scale 100
\font_tt_scale 100
\graphics default
+\default_output_format default
+\output_sync 0
+\bibtex_command default
+\index_command default
\paperfontsize default
\spacing single
\use_hyperref false
@@ -23,9 +31,18 @@
\use_geometry false
\use_amsmath 1
\use_esint 1
+\use_mhchem 1
+\use_mathdots 1
\cite_engine basic
\use_bibtopic false
+\use_indices false
\paperorientation portrait
+\suppress_date false
+\use_refstyle 0
+\index Index
+\shortcut idx
+\color #008000
+\end_index
\secnumdepth 3
\tocdepth 3
\paragraph_separation skip
@@ -36,8 +53,10 @@
\paperpagestyle default
\tracking_changes true
\output_changes true
-\author ""
-\author ""
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict false
+\author 1 "Michael S. Tsirkin"
\end_header
\begin_body
@@ -193,7 +212,7 @@ Each virtqueue occupies two or more physically-contiguous
pages (defined,
\begin_layout Standard
\begin_inset Tabular
<lyxtabular version="3" rows="1"
columns="4">
-<features>
+<features tabularvalignment="middle">
<column alignment="center" valignment="top"
width="0">
<column alignment="center" valignment="top"
width="0">
<column alignment="center" valignment="top"
width="0">
@@ -308,7 +327,7 @@ The Subsystem Device ID indicates which virtio device is
supported by the
\begin_layout Standard
\begin_inset Tabular
<lyxtabular version="3" rows="8"
columns="3">
-<features>
+<features tabularvalignment="middle">
<column alignment="center" valignment="top"
width="0">
<column alignment="center" valignment="top"
width="0">
<column alignment="center" valignment="bottom"
width="0">
@@ -661,7 +680,7 @@ The virtio header looks as follows:
\begin_layout Standard
\begin_inset Tabular
<lyxtabular version="3" rows="4"
columns="9">
-<features>
+<features tabularvalignment="middle">
<column alignment="left" valignment="top"
width="0">
<column alignment="left" valignment="top"
width="0">
<column alignment="left" valignment="top"
width="0">
@@ -953,6 +972,10 @@ ISR
\size footnotesize
Features
+\change_inserted 1 1304329091
+ bits 0:31
+\change_unchanged
+
\end_layout
\end_inset
@@ -964,6 +987,10 @@ Features
\size footnotesize
Features
+\change_inserted 1 1304329086
+ bits 0:31
+\change_unchanged
+
\end_layout
\end_inset
@@ -1050,7 +1077,7 @@ If MSI-X is enabled for the device, two additional fields
immediately follow
\begin_layout Standard
\begin_inset Tabular
<lyxtabular version="3" rows="4"
columns="3">
-<features>
+<features tabularvalignment="middle">
<column alignment="left" valignment="top"
width="0">
<column alignment="left" valignment="top"
width="0">
<column alignment="left" valignment="top"
width="0">
@@ -1186,6 +1213,177 @@ Vector
\end_layout
\begin_layout Standard
+
+\change_inserted 1 1304328924
+Finally, if feature bits (VIRTIO_F_FEATURES_HI) this is immediately followed
+ by two additional fields:
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1 1304328925
+\begin_inset Tabular
+<lyxtabular version="3" rows="4"
columns="3">
+<features tabularvalignment="middle">
+<column alignment="left" valignment="top"
width="0">
+<column alignment="left" valignment="top"
width="0">
+<column alignment="left" valignment="top"
width="0">
+<row>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" rightline="true"
usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+Bits
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+32
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+32
+\end_layout
+
+\end_inset
+</cell>
+</row>
+<row>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" rightline="true"
usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+Read/Write
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+R
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+R+W
+\end_layout
+
+\end_inset
+</cell>
+</row>
+<row>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" rightline="true"
usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+Purpose
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+
+\size footnotesize
+Device
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+
+\size footnotesize
+Guest
+\end_layout
+
+\end_inset
+</cell>
+</row>
+<row>
+<cell alignment="center" valignment="top"
bottomline="true" leftline="true" rightline="true"
usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304328925
+
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
bottomline="true" leftline="true"
usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304329099
+
+\size footnotesize
+Features bits 32:63
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top"
bottomline="true" leftline="true"
usebox="none">
+\begin_inset Text
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304329102
+
+\size footnotesize
+Features bits 32:63
+\end_layout
+
+\end_inset
+</cell>
+</row>
+</lyxtabular>
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
Immediately following these general headers, there may be device-specific
headers:
\end_layout
@@ -1193,7 +1391,7 @@ Immediately following these general headers, there may be
device-specific
\begin_layout Standard
\begin_inset Tabular
<lyxtabular version="3" rows="4"
columns="2">
-<features>
+<features tabularvalignment="middle">
<column alignment="left" valignment="top"
width="0">
<column alignment="left" valignment="top"
width="0">
<row>
@@ -1348,7 +1546,20 @@ Feature Bits
The least significant 31 bits of the first configuration field indicates
the features that the device supports (the high bit is reserved, and will
be used to indicate the presence of future feature bits elsewhere).
- The bits are allocated as follows:
+
+\change_inserted 1 1304331636
+If more than 31 feature bits are supported, the device indicates so by setting
+ feature bit 31 (see
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "cha:Reserved-Feature-Bits"
+
+\end_inset
+
+).
+
+\change_unchanged
+The bits are allocated as follows:
\end_layout
\begin_layout Description
@@ -1372,7 +1583,33 @@ to
\begin_inset space ~
\end_inset
-30 Feature bits reserved for extensions to the queue mechanism
+
+\change_inserted 1 1304329326
+4
+\change_deleted 1 1304329325
+3
+\change_unchanged
+0 Feature bits reserved for extensions to the queue
+\change_inserted 1 1304540448
+and feature negotiation
+\change_unchanged
+mechanism
+\change_inserted 1 1304540449
+s
+\end_layout
+
+\begin_layout Description
+
+\change_inserted 1 1304329398
+41
+\begin_inset space ~
+\end_inset
+
+to
+\begin_inset space ~
+\end_inset
+
+63 Feature bits reserved for future extensions
\end_layout
\begin_layout Standard
@@ -1407,6 +1644,19 @@ This allows for forwards and backwards compatibility: if
the device is enhanced
support, it will not see that feature bit in the Device Features field
and can go into backwards compatibility mode (or, for poor implementations,
set the FAILED Device Status bit).
+\change_inserted 1 1304329423
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1 1304331742
+Access to feature bits 32 to 63 is enabled by Guest by setting feature bit
+ 31.
+ If this bit is unset, Device must assume that all feature bits > 31 are
+ unset.
+\change_unchanged
+
\end_layout
\begin_layout Subsubsection
@@ -1891,7 +2141,38 @@ flags
field is currently 0 or 1: 1 indicating that we do not need an interrupt
when the device consumes a descriptor from the available ring.
- This interrupt suppression is merely an optimization; it may not suppress
+
+\change_inserted 1 1306923367
+Alternatively, the guest can ask the device to delay interrupts until an
+ entry with an index specified by the
+\begin_inset Quotes eld
+\end_inset
+
+used_event
+\begin_inset Quotes erd
+\end_inset
+
+ field is written in the used ring (equivalently, until the
+\emph on
+idx
+\emph default
+ field in the used ring will reach the value
+\emph on
+used_event + 1
+\emph default
+).
+ The method employed by the device is controlled by the VIRTIO_RING_F_EVENT_IDX
+ feature bit (see
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "cha:Reserved-Feature-Bits"
+
+\end_inset
+
+).
+
+\change_unchanged
+This interrupt suppression is merely an optimization; it may not suppress
interrupts entirely.
\end_layout
@@ -1940,6 +2221,17 @@ struct vring_avail {
\begin_layout Plain Layout
u16 ring[qsz]; /* qsz is the Queue Size field read from device */
+\change_inserted 1 1304329945
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304329957
+
+ u16 used_event;
+\change_unchanged
+
\end_layout
\begin_layout Plain Layout
@@ -1963,8 +2255,71 @@ The used ring is where the device returns buffers once it
is done with them.
\emph on
available
\emph default
- ring (the flag is kept here because this is the only part of the virtqueue
- written by the device).
+ ring
+\change_inserted 1 1304540575
+.
+ Alternatively, the
+\begin_inset Quotes eld
+\end_inset
+
+avail_event
+\begin_inset Quotes erd
+\end_inset
+
+ field can be used by the device to hint that no notification is necessary
+ until an entry with an index specified by the
+\begin_inset Quotes eld
+\end_inset
+
+avail_event
+\begin_inset Quotes erd
+\end_inset
+
+ is written in the available ring (equivalently, until the
+\emph on
+idx
+\emph default
+ field in the available ring will reach the value
+\emph on
+avail_event + 1
+\emph default
+).
+
+\change_unchanged
+
+\change_inserted 1 1304540614
+The method employed by the device is controlled by the guest through the
+ VIRTIO_RING_F_EVENT_IDX feature bit (see
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "cha:Reserved-Feature-Bits"
+
+\end_inset
+
+).
+
+\change_deleted 1 1304331235
+(the flag is kept here because this is the only part of the virtqueue written
+ by the device)
+\change_inserted 1 1304540560
+
+\begin_inset Foot
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304331235
+These fields are kept here because this is the only part of the virtqueue
+ written by the device
+\change_unchanged
+
+\end_layout
+
+\end_inset
+
+
+\change_unchanged
+.
\end_layout
\begin_layout Standard
@@ -2046,6 +2401,17 @@ struct vring_used {
\begin_layout Plain Layout
struct vring_used_elem ring[qsz];
+\change_inserted 1 1304330369
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304330380
+
+ u16 avail_event;
+\change_unchanged
+
\end_layout
\begin_layout Plain Layout
@@ -2065,9 +2431,13 @@ Helpers for Managing Virtqueues
\begin_layout Standard
The Linux Kernel Source code contains the definitions above and helper routines
in a more usable form, in include/linux/virtio_ring.h.
- This was explicitly licensed by IBM under the (3-clause) BSD license so
- that it can be freely used by all other projects, and is reproduced (with
- slight variation to remove Linux assumptions) in Appendix A.
+ This was explicitly licensed by IBM
+\change_inserted 1 1304342159
+and Red Hat
+\change_unchanged
+under the (3-clause) BSD license so that it can be freely used by all other
+ projects, and is reproduced (with slight variation to remove Linux
assumptions)
+ in Appendix A.
\end_layout
\begin_layout Section
@@ -2374,12 +2744,61 @@ before
\emph default
checking the suppression flag: it's OK to notify gratuitously, but not
to omit a required notification.
- So again, we use a memory barrier here before reading the flags.
+ So again, we use a memory barrier here before reading the flags
+\change_inserted 1 1304336099
+ or the avail_event field
+\change_unchanged
+.
\end_layout
\begin_layout Standard
-If the VRING_USED_F_NOTIFY flag is not set, we go ahead and write to the
- PCI configuration space.
+If
+\change_inserted 1 1304336234
+the VIRTIO_F_RING_EVENT_IDX feature is not negotiated, and if
+\change_unchanged
+the VRING_USED_F_NOTIFY flag is not set, we go ahead and write to the PCI
+ configuration space.
+\change_inserted 1 1304336255
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1 1304336617
+If the VIRTIO_F_RING_EVENT_IDX feature is negotiated, we read the avail_event
+ field in the available ring structure.
+ If the available index crossed_the
+\emph on
+avail_event
+\emph default
+ field value since the last notification, we go ahead and write to the PCI
+ configuration space.
+ The
+\emph on
+avail_event
+\emph default
+ field wraps naturally at 65536 as well:
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1 1304336524
+\begin_inset listings
+inline false
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304336569
+
+(u16)(new_idx - avail_event - 1) < (u16)(new_idx - old_idx)
+\end_layout
+
+\end_inset
+
+
+\change_unchanged
+
\end_layout
\begin_layout Subsection
@@ -2408,8 +2827,66 @@ Update the used ring idx.
\end_layout
\begin_layout Enumerate
-If the VRING_AVAIL_F_NO_INTERRUPT flag is not set in avail\SpecialChar
\nobreakdash-
->flags:
+
+\change_inserted 1 1304336736
+Determine whether an interrupt is necessary:
+\end_layout
+
+\begin_deeper
+\begin_layout Enumerate
+
+\change_inserted 1 1306923440
+If the VIRTIO_F_RING_EVENT_IDX feature is not negotiated: check if
+\change_deleted 1 1304336781
+I
+\change_unchanged
+f the VRING_AVAIL_F_NO_INTERRUPT flag is not set in avail\SpecialChar
\nobreakdash-
+>flags
+\change_inserted 1 1304336788
+
+\end_layout
+
+\begin_layout Enumerate
+
+\change_deleted 1 1304336785
+:
+\change_inserted 1 1306923443
+If the VIRTIO_F_RING_EVENT_IDX feature is negotiated: check whether the
+ used index crossed the
+\emph on
+used_event
+\emph default
+ field value since the last update.
+ The
+\emph on
+used_event
+\emph default
+ field wraps naturally at 65536 as well:
+\begin_inset listings
+inline false
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304336902
+
+(u16)(new_idx - used_event - 1) < (u16)(new_idx - old_idx)
+\end_layout
+
+\end_inset
+
+
+\change_unchanged
+
+\end_layout
+
+\end_deeper
+\begin_layout Enumerate
+
+\change_inserted 1 1304336714
+If an interrupt is necessary:
+\change_unchanged
+
\end_layout
\begin_deeper
@@ -2464,13 +2941,87 @@ If MSI-X capability is enabled: look through the used
rings of each virtqueue
\end_layout
\begin_layout Standard
+
+\change_inserted 1 1306923408
+For each ring, guest should then disable interrupts by writing
VRING_AVAIL_F_NO_
+INTERRUPT flag in avail structure, if required.
+ It can then process used ring entries finally enabling interrupts by clearing
+ the VRING_AVAIL_F_NO_INTERRUPT flag or updating the EVENT_IDX field in
+ the available structure, Guest should then execute a memory barrier, and
+ then recheck the ring empty condition.
+ This is necessary to handle the case where, after the last check and before
+ enabling interrupts, an interrupt has been suppressed by the device:
+\end_layout
+
+\begin_layout Standard
\begin_inset listings
inline false
status open
\begin_layout Plain Layout
-while (vq->last_seen_used != vring->used.idx) {
+\change_inserted 1 1304342051
+
+vring_disable_interrupts(vq);
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341878
+
+for (;;) {
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341880
+
+ if
+\change_deleted 1 1304341882
+while
+\change_unchanged
+(vq->last_seen_used != vring->used.idx) {
+\change_inserted 1 1304341888
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304342047
+
+ vring_enable_interrupts(vq);
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341986
+
+ mb();
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341964
+
+ if (vq->last_seen_used != vring->used.idx)
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341974
+
+ break;
+\change_unchanged
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341887
+
+ }
+\change_unchanged
+
\end_layout
\begin_layout Plain Layout
@@ -2668,6 +3219,7 @@ Clusters of functionality which are always implemented
together can use
\begin_layout Standard
\begin_inset CommandInset nomencl_print
LatexCommand printnomenclature
+set_width "none"
\end_inset
@@ -2721,6 +3273,15 @@ status open
\begin_layout Plain Layout
* Copyright 2007, 2009, IBM Corporation
+\change_inserted 1 1304341032
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341075
+
+ * Copyright 2011, Red Hat, Inc
\end_layout
\begin_layout Plain Layout
@@ -3019,6 +3580,17 @@ struct vring_avail {
\begin_layout Plain Layout
uint16_t ring[];
+\change_inserted 1 1304340808
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304340816
+
+ uint16_t used_event;
+\change_unchanged
+
\end_layout
\begin_layout Plain Layout
@@ -3090,6 +3662,17 @@ struct vring_used {
\begin_layout Plain Layout
struct vring_used_elem ring[];
+\change_inserted 1 1304340824
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304340831
+
+ uint16_t avail_event;
+\change_unchanged
+
\end_layout
\begin_layout Plain Layout
@@ -3227,7 +3810,13 @@ struct vring {
\begin_layout Plain Layout
- * __u16 used_idx;
+ * __u16
+\change_inserted 1 1306923408
+EVENT_IDX
+\change_deleted 1 1306923408
+used_idx
+\change_unchanged
+;
\end_layout
\begin_layout Plain Layout
@@ -3326,12 +3915,58 @@ static inline unsigned vring_size(unsigned int num,
unsigned long align)
\begin_layout Plain Layout
- + sizeof(uint16_t)*2 + sizeof(struct vring_used_elem)*num;
+ + sizeof(uint16_t)*
+\change_deleted 1 1304340844
+2
+\change_inserted 1 1304340844
+3
+\change_unchanged
+ + sizeof(struct vring_used_elem)*num;
+\end_layout
+
+\begin_layout Plain Layout
+
+}
+\change_inserted 1 1304340918
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304340918
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304340987
+
+static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx,
+ uint16_t old_idx)
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304340944
+
+{
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1 1304341001
+
+ return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx
+ - old_idx);
\end_layout
\begin_layout Plain Layout
+\change_inserted 1 1304340938
+
}
+\change_unchanged
+
\end_layout
\begin_layout Plain Layout
@@ -3355,7 +3990,13 @@ Appendix B: Reserved Feature Bits
\end_layout
\begin_layout Standard
-Currently there are three device-independent feature bits defined:
+Currently there are
+\change_inserted 1 1306923235
+five
+\change_deleted 1 1304330657
+three
+\change_unchanged
+ device-independent feature bits defined:
\end_layout
\begin_layout Description
@@ -3365,7 +4006,11 @@ VIRTIO_F_NOTIFY_ON_EMPTY
(24) Negotiating this feature indicates that the driver wants an interrupt
if the device runs out of available descriptors on a virtqueue, even though
- interrupts are suppressed using the VRING_AVAIL_F_NO_INTERRUPT flag.
+ interrupts are suppressed using the VRING_AVAIL_F_NO_INTERRUPT flag
+\change_inserted 1 1304341161
+ or the used_event field
+\change_unchanged
+.
An example of this is the networking driver: it doesn't need to know every
time a packet is transmitted, but it does need to free the transmitted
packets a finite time after they are transmitted.
@@ -3390,6 +4035,53 @@ reference "sub:Indirect-Descriptors"
\end_layout
\begin_layout Description
+
+\change_inserted 1 1306923206
+VIRTIO_F_RING_EVENT_IDX(29) This feature enables the
+\emph on
+used_event
+\emph default
+ and the
+\emph on
+avail_event
+\emph default
+ fields.
+ If set, it indicates that the device should ignore the
+\emph on
+flags
+\emph default
+ field in the available ring structure.
+ Instead, the
+\emph on
+ used_event
+\emph default
+ field in this structure is used by guest to suppress device interrupts.
+ Further, the driver should ignore the
+\emph on
+flags
+\emph default
+ field in the used ring structure.
+ Instead, the
+\emph on
+avail_event
+\emph default
+ field in this structure is used by the device to suppress notifications.
+ If unset, the driver should ignore the
+\emph on
+used_event
+\emph default
+ field; the device should ignore the
+\emph on
+avail_event
+\emph default
+ field; the
+\emph on
+flags
+\emph default
+ field is used
+\end_layout
+
+\begin_layout Description
VIRTIO_F_BAD_FEATURE(30) This feature should never be negotiated by the
guest; doing so is an indication that the guest is faulty
\begin_inset Foot
@@ -3403,6 +4095,16 @@ An experimental virtio PCI driver contained in Linux
version 2.6.25 had this
\end_inset
+\change_inserted 1 1304330854
+
+\end_layout
+
+\begin_layout Description
+
+\change_inserted 1 1304330961
+VIRTIO_F_FEATURES_HIGH(31) This feature indicates that the device supports
+ feature bits 32:63.
+ If unset, feature bits 32:63 are unset.
\end_layout
\begin_layout Chapter*
--
1.7.5.53.gc233e
Rusty Russell
2011-Jun-02 01:49 UTC
[PATCHv3] virtio-spec: 64 bit features, used/avail event, fixes
On Wed, 1 Jun 2011 13:25:48 +0300, "Michael S. Tsirkin" <mst at redhat.com> wrote:> Add an option to modify the notificatin > hand-off in virtio to be basically like Xen: > each side published an index, the other side only triggers > an event when it crosses that index value > (Xen event indexes start at 1, ours start at 0 for > backward-compatiblity, but that's minor). > > Since we've run out of bits in the 32 bit field, > I added another 32 bit and bit 31 enables that.OK. I've applied this, and published it as the 0.9 draft. Thanks! Rusty.
Michael S. Tsirkin
2011-Aug-03 16:29 UTC
[PATCHv3] virtio-spec: 64 bit features, used/avail event, fixes
On Wed, Aug 03, 2011 at 06:15:33PM +0200, Gerd Hoffmann wrote:> Hi, > > >E.g. with 32 bridges, and 32 devices behind each one, > >the available 64K space gets us only 64 bytes per device. > > 15 bridges (with io window enabled) max, the smallest io window you > can assign to a bridge is 4k,Hmm true, I missed that. So with 32 devs we get 256 bytes per device. We can still get low on that space when using multifunction devices though (there could be up to 256 functions behind a bridge, which only leaves 16 bytes per device). BTW, this limitation will be a problem for pci express devices.> and you need some space for the > devices on the root bus ... > > cheers, > Gerd
Michael S. Tsirkin
2011-Aug-03 16:39 UTC
[PATCHv3] virtio-spec: 64 bit features, used/avail event, fixes
On Wed, Aug 03, 2011 at 06:15:33PM +0200, Gerd Hoffmann wrote:> Hi, > > >E.g. with 32 bridges, and 32 devices behind each one, > >the available 64K space gets us only 64 bytes per device. > > 15 bridges (with io window enabled) max, the smallest io window you > can assign to a bridge is 4k, and you need some space for the > devices on the root bus ... > > cheers, > GerdHmm, wait, we could go 32 bit, then we are not limited to 32 bridges anymore, right? Does our bios support that? -- MST