Commit a31ca6801c ("qemu/queue.h: clear linked list pointers on
remove") revealed that a request was removed twice from a list, once
in xen_block_finish_request() and a second time in
xen_block_release_request() when both function are called from
xen_block_complete_aio(). But also, the `requests_inflight' counter is
decreased twice, and thus became negative.
This is a bug that was introduced in bfd0d63660 ("xen-block: improve
response latency"), where a `finished' list was removed.
That commit also introduced a leak of request in xen_block_do_aio().
That function calls xen_block_finish_request() but the request is
never released after that.
To fix both issue, we do two changes:
- we squash finish_request() and release_request() together as we want
to remove a request from 'inflight' list to add it to 'freelist'.
- before releasing a request, we need to let the other end know the
result, thus we should call xen_block_send_response() before
releasing a request.
The first change fixes the double QLIST_REMOVE() as we remove the extra
call. The second change makes the leak go away because if we want to
call finish_request(), we need to call a function that does all of
finish, send response, and release.
Fixes: bfd0d63660 ("xen-block: improve response latency")
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20200406140217.1441858-1-anthony.perard@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>
[mreitz: Amended commit message as per Paul's suggestions]
Signed-off-by: Max Reitz <mreitz@redhat.com>
It is not safe to close an event channel from the QEMU main thread when
that channel's poller is running in IOThread context.
This patch adds a new xen_device_set_event_channel_context() function
to explicitly assign the channel AioContext, and modifies
xen_device_bind_event_channel() to initially assign the channel's poller
to the QEMU main thread context. The code in xen-block's dataplane is
then modified to assign the channel to IOThread context during
xen_block_dataplane_start() and de-assign it during in
xen_block_dataplane_stop(), such that the channel is always assigned
back to main thread context before it is closed. aio_set_fd_handler()
already deals with all the necessary synchronization when moving an fd
between AioContext-s so no extra code is needed to manage this.
Reported-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20191216143451.19024-1-pdurrant@amazon.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
In my "build everything" tree, changing qemu/main-loop.h triggers a
recompile of some 5600 out of 6600 objects (not counting tests and
objects that don't depend on qemu/osdep.h). It includes block/aio.h,
which in turn includes qemu/event_notifier.h, qemu/notify.h,
qemu/processor.h, qemu/qsp.h, qemu/queue.h, qemu/thread-posix.h,
qemu/thread.h, qemu/timer.h, and a few more.
Include qemu/main-loop.h only where it's needed. Touching it now
recompiles only some 1700 objects. For block/aio.h and
qemu/event_notifier.h, these numbers drop from 5600 to 2800. For the
others, they shrink only slightly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190812052359.30071-21-armbru@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
In my "build everything" tree, changing hw/hw.h triggers a recompile
of some 2600 out of 6600 objects (not counting tests and objects that
don't depend on qemu/osdep.h).
The previous commits have left only the declaration of hw_error() in
hw/hw.h. This permits dropping most of its inclusions. Touching it
now recompiles less than 200 objects.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20190812052359.30071-19-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
This patch introduces a poll callback for event channel fd-s and uses
this to invoke the channel callback function.
To properly support polling, it is necessary for the event channel callback
function to return a boolean saying whether it has done any useful work or
not. Thus xen_block_dataplane_event() is modified to directly invoke
xen_block_handle_requests() and the latter only returns true if it actually
processes any requests. This also means that the call to qemu_bh_schedule()
is moved into xen_block_complete_aio(), which is more intuitive since the
only reason for doing a deferred poll of the shared ring should be because
there were previously insufficient resources to fully complete a previous
poll.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20190408151617.13025-4-paul.durrant@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This patch adds an AioContext parameter to xen_device_bind_event_channel()
and then uses aio_set_fd_handler() to set the callback rather than
qemu_set_fd_handler().
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20190408151617.13025-3-paul.durrant@citrix.com>
[Call aio_set_fd_handler() with is_external=true]
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
A recent Xen commit [1] clarified the semantics of sector based quantities
used in the blkif protocol such that it is now safe to create a xen-block
device with a logical_block_size != 512, as long as the device only
connects to a frontend advertizing 'feature-large-block-size'.
This patch modifies xen-block accordingly. It also uses a stack variable
for the BlockBackend in xen_block_realize() to avoid repeated dereferencing
of the BlockConf pointer, and changes the parameters of
xen_block_dataplane_create() so that the BlockBackend pointer and sector
size are passed expicitly rather than implicitly via the BlockConf.
These modifications have been tested against a recent Windows PV XENVBD
driver [2] using a xen-disk device with a 4kB logical block size.
[1] http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=67e1c050e36b2c9900cca83618e56189effbad98
[2] https://winpvdrvbuild.xenproject.org:8080/job/XENVBD-master/126
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20190409164038.25484-1-paul.durrant@citrix.com>
[Edited error message]
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Add an Error parameter to blk_set_aio_context() and use
bdrv_child_try_set_aio_context() internally to check whether all
involved nodes can actually support the AioContext switch.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
The Xen blkif protocol requires that sector based quantities should be
interpreted strictly as multiples of 512 bytes. Specifically:
"first_sect and last_sect in blkif_request_segment, as well as
sector_number in blkif_request, are always expressed in 512-byte units."
Commit fcab2b464e "xen: add header and build dataplane/xen-block.c"
incorrectly modified behaviour to use the block device logical_block_size
property as the scale, instead of correctly shifting values by the
hardcoded BDRV_SECTOR_BITS (and hence scaling them to 512 byte units).
This patch undoes that change and restores compliance with the spec.
Furthermore, this patch also restores the original xen_disk behaviour
of advertizing a hardcoded 'sector-size' value of 512 in xenstore and
scaling 'sectors' accordingly. The realize() method is also modified to
fail if logical_block_size is set to anything other than 512.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20190401121719.27208-1-paul.durrant@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
The if() statement is clearly bogus (dead code which should have been
cleaned up when grant mapping was removed).
Spotted by Coverity: CID 1398635
While in the neighbourhood, add a missing 'fall through' annotation.
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20190215162533.19475-2-paul.durrant@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Some frontend drivers will handle dynamic resizing of PV disks, so set up
the BlockDevOps resize_cb() method during xen_block_realize() to allow
this to be done.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
The xen-block dataplane currently allocates memory to hold the data for
each request as that request is used, and frees it afterwards. Because
it requires page-aligned blocks, this interacts poorly with non-page-
aligned allocations and balloons the heap.
Instead, allocate the maximum possible buffer size required for the
protocol, which is BLKIF_MAX_SEGMENTS_PER_REQUEST (currently 11) pages
when the request structure is created, and keep that buffer until it is
destroyed. Since the requests are re-used via a free list, this should
actually improve memory usage.
Signed-off-by: Tim Smith <tim.smith@citrix.com>
Re-based and commit comment adjusted.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
If the I/O ring is full, the guest cannot send any more requests
until some responses are sent. Only sending all available responses
just before checking for new work does not leave much time for the
guest to supply new work, so this will cause stalls if the ring gets
full. Also, not completing reads as soon as possible adds latency
to the guest.
To alleviate that, complete IO requests as soon as they come back.
xen_block_send_response() already returns a value indicating whether
a notify should be sent, which is all the batching we need.
Signed-off-by: Tim Smith <tim.smith@citrix.com>
Re-based and commit comment adjusted.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
When I/O consists of many small requests, performance is improved by
batching them together in a single io_submit() call. When there are
relatively few requests, the extra overhead is not worth it. This
introduces a check to start batching I/O requests via blk_io_plug()/
blk_io_unplug() in an amount proportional to the number which were
already in flight at the time we started reading the ring.
Signed-off-by: Tim Smith <tim.smith@citrix.com>
Re-based and commit comment adjusted.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This is a purely cosmetic patch that purges remaining use of 'blk' and
'ioreq' in local function names, and then makes sure all functions are
prefixed with 'xen_block_'.
No functional change.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This is a purely cosmetic patch that purges the name 'ioreq' from struct,
variable and field names. (This name has been problematic for a long time
as 'ioreq' is the name used for generic I/O requests coming from Xen).
The patch replaces 'struct ioreq' with a new 'XenBlockRequest' type and
'ioreq' field/variable names with 'request', and then does necessary
fix-up to adhere to coding style.
Function names are not modified by this patch. They will be dealt with in
a subsequent patch.
No functional change.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This is a purely cosmetic patch that substitutes the old 'struct XenBlkDev'
name with 'XenBlockDataPlane' and 'blkdev' field/variable names with
'dataplane', and then does necessary fix-up to adhere to coding style.
No functional change.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This patch adds the transformations necessary to get dataplane/xen-block.c
to build against the new XenBus/XenDevice framework. MAINTAINERS is also
updated due to the introduction of dataplane/xen-block.h.
NOTE: Existing data structure names are retained for the moment. These will
be modified by subsequent patches. A typedef for XenBlockDataPlane
has been added to the header (based on the old struct XenBlkDev name
for the moment) so that the old names don't need to leak out of the
dataplane code.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Not all of the code duplicated from xen_disk.c is required as the basis for
the new dataplane implementation so this patch removes extraneous code,
along with the legacy #includes and calls to the legacy xen_pv_printf()
function. Error messages are changed to be reported using error_report().
NOTE: The code is still not yet built. Further transformations will be
required to make it correctly interface to the new XenBus/XenDevice
framework. They will be delivered in a subsequent patch.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
The new xen-block XenDevice implementation requires the same core
dataplane as the legacy xen_disk implementation it will eventually replace.
This patch therefore copies the legacy xen_disk.c source module into a new
dataplane/xen-block.c source module as the basis for the new dataplane and
adjusts the MAINTAINERS file accordingly.
NOTE: The duplicated code is not yet built. It is simply put into place by
this patch (just fixing style violations) such that the
modifications that will need to be made to the code are not
conflated with code movement, thus making review harder.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
