</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-h264-vui-sar-idc">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_IDC</constant> </entry>
<entry>enum v4l2_mpeg_video_h264_vui_sar_idc</entry>
</row>
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-h264-level">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_H264_LEVEL</constant> </entry>
<entry>enum v4l2_mpeg_video_h264_level</entry>
</row>
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-mpeg4-level">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_MPEG4_LEVEL</constant> </entry>
<entry>enum v4l2_mpeg_video_mpeg4_level</entry>
</row>
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-h264-profile">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_H264_PROFILE</constant> </entry>
- <entry>enum v4l2_mpeg_h264_profile</entry>
+ <entry>enum v4l2_mpeg_video_h264_profile</entry>
</row>
<row><entry spanname="descr">The profile information for H264.
Applicable to the H264 encoder.
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-mpeg4-profile">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_MPEG4_PROFILE</constant> </entry>
- <entry>enum v4l2_mpeg_mpeg4_profile</entry>
+ <entry>enum v4l2_mpeg_video_mpeg4_profile</entry>
</row>
<row><entry spanname="descr">The profile information for MPEG4.
Applicable to the MPEG4 encoder.
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-multi-slice-mode">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE</constant> </entry>
- <entry>enum v4l2_mpeg_multi_slice_mode</entry>
+ <entry>enum v4l2_mpeg_video_multi_slice_mode</entry>
</row>
<row><entry spanname="descr">Determines how the encoder should handle division of frame into slices.
Applicable to the encoder.
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-h264-loop-filter-mode">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_MODE</constant> </entry>
- <entry>enum v4l2_mpeg_h264_loop_filter_mode</entry>
+ <entry>enum v4l2_mpeg_video_h264_loop_filter_mode</entry>
</row>
<row><entry spanname="descr">Loop filter mode for H264 encoder.
Possible values are:</entry>
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-h264-entropy-mode">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_H264_ENTROPY_MODE</constant> </entry>
- <entry>enum v4l2_mpeg_h264_symbol_mode</entry>
+ <entry>enum v4l2_mpeg_video_h264_entropy_mode</entry>
</row>
<row><entry spanname="descr">Entropy coding mode for H264 - CABAC/CAVALC.
Applicable to the H264 encoder.
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-video-header-mode">
<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_HEADER_MODE</constant> </entry>
- <entry>enum v4l2_mpeg_header_mode</entry>
+ <entry>enum v4l2_mpeg_video_header_mode</entry>
</row>
<row><entry spanname="descr">Determines whether the header is returned as the first buffer or is
it returned together with the first frame. Applicable to encoders.
Applicable to the H264 encoder.</entry>
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-mfc51-video-frame-skip-mode">
<entry spanname="id"><constant>V4L2_CID_MPEG_MFC51_VIDEO_FRAME_SKIP_MODE</constant> </entry>
- <entry>enum v4l2_mpeg_mfc51_frame_skip_mode</entry>
+ <entry>enum v4l2_mpeg_mfc51_video_frame_skip_mode</entry>
</row>
<row><entry spanname="descr">
Indicates in what conditions the encoder should skip frames. If encoding a frame would cause the encoded stream to be larger then
</entry>
</row>
<row><entry></entry></row>
- <row>
+ <row id="v4l2-mpeg-mfc51-video-force-frame-type">
<entry spanname="id"><constant>V4L2_CID_MPEG_MFC51_VIDEO_FORCE_FRAME_TYPE</constant> </entry>
- <entry>enum v4l2_mpeg_mfc51_force_frame_type</entry>
+ <entry>enum v4l2_mpeg_mfc51_video_force_frame_type</entry>
</row>
<row><entry spanname="descr">Force a frame type for the next queued buffer. Applicable to encoders.
Possible values are:</entry>
bridges). In order to ensure that all the data has arrived in memory,
the interrupt handler must read a register on the device which raised
the interrupt. PCI transaction ordering rules require that all the data
-arrives in memory before the value can be returned from the register.
+arrive in memory before the value may be returned from the register.
Using MSIs avoids this problem as the interrupt-generating write cannot
pass the data writes, so by the time the interrupt is raised, the driver
knows that all the data has arrived in memory.
int pci_enable_msi(struct pci_dev *dev)
-A successful call will allocate ONE interrupt to the device, regardless
-of how many MSIs the device supports. The device will be switched from
+A successful call allocates ONE interrupt to the device, regardless
+of how many MSIs the device supports. The device is switched from
pin-based interrupt mode to MSI mode. The dev->irq number is changed
-to a new number which represents the message signaled interrupt.
-This function should be called before the driver calls request_irq()
-since enabling MSIs disables the pin-based IRQ and the driver will not
-receive interrupts on the old interrupt.
+to a new number which represents the message signaled interrupt;
+consequently, this function should be called before the driver calls
+request_irq(), because an MSI is delivered via a vector that is
+different from the vector of a pin-based interrupt.
4.2.2 pci_enable_msi_block
If this function returns a negative number, it indicates an error and
the driver should not attempt to request any more MSI interrupts for
-this device. If this function returns a positive number, it will be
-less than 'count' and indicate the number of interrupts that could have
-been allocated. In neither case will the irq value have been
-updated, nor will the device have been switched into MSI mode.
+this device. If this function returns a positive number, it is
+less than 'count' and indicates the number of interrupts that could have
+been allocated. In neither case is the irq value updated or the device
+switched into MSI mode.
The device driver must decide what action to take if
-pci_enable_msi_block() returns a value less than the number asked for.
-Some devices can make use of fewer interrupts than the maximum they
-request; in this case the driver should call pci_enable_msi_block()
+pci_enable_msi_block() returns a value less than the number requested.
+For instance, the driver could still make use of fewer interrupts;
+in this case the driver should call pci_enable_msi_block()
again. Note that it is not guaranteed to succeed, even when the
'count' has been reduced to the value returned from a previous call to
pci_enable_msi_block(). This is because there are multiple constraints
on the number of vectors that can be allocated; pci_enable_msi_block()
-will return as soon as it finds any constraint that doesn't allow the
+returns as soon as it finds any constraint that doesn't allow the
call to succeed.
4.2.3 pci_disable_msi
interrupt(s). The interrupt may subsequently be assigned to another
device, so drivers should not cache the value of dev->irq.
-A device driver must always call free_irq() on the interrupt(s)
-for which it has called request_irq() before calling this function.
-Failure to do so will result in a BUG_ON(), the device will be left with
-MSI enabled and will leak its vector.
+Before calling this function, a device driver must always call free_irq()
+on any interrupt for which it previously called request_irq().
+Failure to do so results in a BUG_ON(), leaving the device with
+MSI enabled and thus leaking its vector.
4.3 Using MSI-X
};
This allows for the device to use these interrupts in a sparse fashion;
-for example it could use interrupts 3 and 1027 and allocate only a
+for example, it could use interrupts 3 and 1027 and yet allocate only a
two-element array. The driver is expected to fill in the 'entry' value
-in each element of the array to indicate which entries it wants the kernel
-to assign interrupts for. It is invalid to fill in two entries with the
+in each element of the array to indicate for which entries the kernel
+should assign interrupts; it is invalid to fill in two entries with the
same number.
4.3.1 pci_enable_msix
Calling this function asks the PCI subsystem to allocate 'nvec' MSIs.
The 'entries' argument is a pointer to an array of msix_entry structs
which should be at least 'nvec' entries in size. On success, the
-function will return 0 and the device will have been switched into
-MSI-X interrupt mode. The 'vector' elements in each entry will have
-been filled in with the interrupt number. The driver should then call
-request_irq() for each 'vector' that it decides to use.
+device is switched into MSI-X mode and the function returns 0.
+The 'vector' member in each entry is populated with the interrupt number;
+the driver should then call request_irq() for each 'vector' that it
+decides to use. The device driver is responsible for keeping track of the
+interrupts assigned to the MSI-X vectors so it can free them again later.
If this function returns a negative number, it indicates an error and
the driver should not attempt to allocate any more MSI-X interrupts for
This function, in contrast with pci_enable_msi(), does not adjust
dev->irq. The device will not generate interrupts for this interrupt
-number once MSI-X is enabled. The device driver is responsible for
-keeping track of the interrupts assigned to the MSI-X vectors so it can
-free them again later.
+number once MSI-X is enabled.
Device drivers should normally call this function once per device
during the initialization phase.
-It is ideal if drivers can cope with a variable number of MSI-X interrupts,
+It is ideal if drivers can cope with a variable number of MSI-X interrupts;
there are many reasons why the platform may not be able to provide the
-exact number a driver asks for.
+exact number that a driver asks for.
A request loop to achieve that might look like:
void pci_disable_msix(struct pci_dev *dev)
-This API should be used to undo the effect of pci_enable_msix(). It frees
+This function should be used to undo the effect of pci_enable_msix(). It frees
the previously allocated message signaled interrupts. The interrupts may
subsequently be assigned to another device, so drivers should not cache
the value of the 'vector' elements over a call to pci_disable_msix().
-A device driver must always call free_irq() on the interrupt(s)
-for which it has called request_irq() before calling this function.
-Failure to do so will result in a BUG_ON(), the device will be left with
-MSI enabled and will leak its vector.
+Before calling this function, a device driver must always call free_irq()
+on any interrupt for which it previously called request_irq().
+Failure to do so results in a BUG_ON(), leaving the device with
+MSI-X enabled and thus leaking its vector.
4.3.3 The MSI-X Table
4.4 Handling devices implementing both MSI and MSI-X capabilities
If a device implements both MSI and MSI-X capabilities, it can
-run in either MSI mode or MSI-X mode but not both simultaneously.
+run in either MSI mode or MSI-X mode, but not both simultaneously.
This is a requirement of the PCI spec, and it is enforced by the
PCI layer. Calling pci_enable_msi() when MSI-X is already enabled or
-pci_enable_msix() when MSI is already enabled will result in an error.
+pci_enable_msix() when MSI is already enabled results in an error.
If a device driver wishes to switch between MSI and MSI-X at runtime,
it must first quiesce the device, then switch it back to pin-interrupt
mode, before calling pci_enable_msi() or pci_enable_msix() and resuming
above, MSI-X supports any number of interrupts between 1 and 2048.
In constrast, MSI is restricted to a maximum of 32 interrupts (and
must be a power of two). In addition, the MSI interrupt vectors must
-be allocated consecutively, so the system may not be able to allocate
+be allocated consecutively, so the system might not be able to allocate
as many vectors for MSI as it could for MSI-X. On some platforms, MSI
interrupts must all be targeted at the same set of CPUs whereas MSI-X
interrupts can all be targeted at different CPUs.
Using 'lspci -v' (as root) may show some devices with "MSI", "Message
Signalled Interrupts" or "MSI-X" capabilities. Each of these capabilities
-has an 'Enable' flag which will be followed with either "+" (enabled)
+has an 'Enable' flag which is followed with either "+" (enabled)
or "-" (disabled).
Some host chipsets simply don't support MSIs properly. If we're
lucky, the manufacturer knows this and has indicated it in the ACPI
-FADT table. In this case, Linux will automatically disable MSIs.
+FADT table. In this case, Linux automatically disables MSIs.
Some boards don't include this information in the table and so we have
to detect them ourselves. The complete list of these is found near the
quirk_disable_all_msi() function in drivers/pci/quirks.c.
PCI configuration space (especially the Hypertransport chipsets such
as the nVidia nForce and Serverworks HT2000). As with host chipsets,
Linux mostly knows about them and automatically enables MSIs if it can.
-If you have a bridge which Linux doesn't yet know about, you can enable
+If you have a bridge unknown to Linux, you can enable
MSIs in configuration space using whatever method you know works, then
enable MSIs on that bridge by doing:
0000:00:0e.0).
To disable MSIs, echo 0 instead of 1. Changing this value should be
-done with caution as it can break interrupt handling for all devices
+done with caution as it could break interrupt handling for all devices
below this bridge.
Again, please notify linux-pci@vger.kernel.org of any bridges that need
5.3. Disabling MSIs on a single device
Some devices are known to have faulty MSI implementations. Usually this
-is handled in the individual device driver but occasionally it's necessary
+is handled in the individual device driver, but occasionally it's necessary
to handle this with a quirk. Some drivers have an option to disable use
of MSI. While this is a convenient workaround for the driver author,
it is not good practise, and should not be emulated.
have enabled CONFIG_PCI_MSI.
Then, 'lspci -t' gives the list of bridges above a device. Reading
-/sys/bus/pci/devices/*/msi_bus will tell you whether MSI are enabled (1)
+/sys/bus/pci/devices/*/msi_bus will tell you whether MSIs are enabled (1)
or disabled (0). If 0 is found in any of the msi_bus files belonging
to bridges between the PCI root and the device, MSIs are disabled.
to IOPS mode and starts providing fairness in terms of number of requests
dispatched. Note that this mode switching takes effect only for group
scheduling. For non-cgroup users nothing should change.
+
+CFQ IO scheduler Idling Theory
+===============================
+Idling on a queue is primarily about waiting for the next request to come
+on same queue after completion of a request. In this process CFQ will not
+dispatch requests from other cfq queues even if requests are pending there.
+
+The rationale behind idling is that it can cut down on number of seeks
+on rotational media. For example, if a process is doing dependent
+sequential reads (next read will come on only after completion of previous
+one), then not dispatching request from other queue should help as we
+did not move the disk head and kept on dispatching sequential IO from
+one queue.
+
+CFQ has following service trees and various queues are put on these trees.
+
+ sync-idle sync-noidle async
+
+All cfq queues doing synchronous sequential IO go on to sync-idle tree.
+On this tree we idle on each queue individually.
+
+All synchronous non-sequential queues go on sync-noidle tree. Also any
+request which are marked with REQ_NOIDLE go on this service tree. On this
+tree we do not idle on individual queues instead idle on the whole group
+of queues or the tree. So if there are 4 queues waiting for IO to dispatch
+we will idle only once last queue has dispatched the IO and there is
+no more IO on this service tree.
+
+All async writes go on async service tree. There is no idling on async
+queues.
+
+CFQ has some optimizations for SSDs and if it detects a non-rotational
+media which can support higher queue depth (multiple requests at in
+flight at a time), then it cuts down on idling of individual queues and
+all the queues move to sync-noidle tree and only tree idle remains. This
+tree idling provides isolation with buffered write queues on async tree.
+
+FAQ
+===
+Q1. Why to idle at all on queues marked with REQ_NOIDLE.
+
+A1. We only do tree idle (all queues on sync-noidle tree) on queues marked
+ with REQ_NOIDLE. This helps in providing isolation with all the sync-idle
+ queues. Otherwise in presence of many sequential readers, other
+ synchronous IO might not get fair share of disk.
+
+ For example, if there are 10 sequential readers doing IO and they get
+ 100ms each. If a REQ_NOIDLE request comes in, it will be scheduled
+ roughly after 1 second. If after completion of REQ_NOIDLE request we
+ do not idle, and after a couple of milli seconds a another REQ_NOIDLE
+ request comes in, again it will be scheduled after 1second. Repeat it
+ and notice how a workload can lose its disk share and suffer due to
+ multiple sequential readers.
+
+ fsync can generate dependent IO where bunch of data is written in the
+ context of fsync, and later some journaling data is written. Journaling
+ data comes in only after fsync has finished its IO (atleast for ext4
+ that seemed to be the case). Now if one decides not to idle on fsync
+ thread due to REQ_NOIDLE, then next journaling write will not get
+ scheduled for another second. A process doing small fsync, will suffer
+ badly in presence of multiple sequential readers.
+
+ Hence doing tree idling on threads using REQ_NOIDLE flag on requests
+ provides isolation from multiple sequential readers and at the same
+ time we do not idle on individual threads.
+
+Q2. When to specify REQ_NOIDLE
+A2. I would think whenever one is doing synchronous write and not expecting
+ more writes to be dispatched from same context soon, should be able
+ to specify REQ_NOIDLE on writes and that probably should work well for
+ most of the cases.
projects / linux-2.6.git / commitdiff