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path: root/drivers/block/xen-blkback
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2012-01-10Merge branch 'stable/for-linus-3.3' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen * 'stable/for-linus-3.3' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen: (37 commits) xen/pciback: Expand the warning message to include domain id. xen/pciback: Fix "device has been assigned to X domain!" warning xen/pciback: Move the PCI_DEV_FLAGS_ASSIGNED ops to the "[un|]bind" xen/xenbus: don't reimplement kvasprintf via a fixed size buffer xenbus: maximum buffer size is XENSTORE_PAYLOAD_MAX xen/xenbus: Reject replies with payload > XENSTORE_PAYLOAD_MAX. Xen: consolidate and simplify struct xenbus_driver instantiation xen-gntalloc: introduce missing kfree xen/xenbus: Fix compile error - missing header for xen_initial_domain() xen/netback: Enable netback on HVM guests xen/grant-table: Support mappings required by blkback xenbus: Use grant-table wrapper functions xenbus: Support HVM backends xen/xenbus-frontend: Fix compile error with randconfig xen/xenbus-frontend: Make error message more clear xen/privcmd: Remove unused support for arch specific privcmp mmap xen: Add xenbus_backend device xen: Add xenbus device driver xen: Add privcmd device driver xen/gntalloc: fix reference counts on multi-page mappings ...
2012-01-04Xen: consolidate and simplify struct xenbus_driver instantiationJan Beulich
The 'name', 'owner', and 'mod_name' members are redundant with the identically named fields in the 'driver' sub-structure. Rather than switching each instance to specify these fields explicitly, introduce a macro to simplify this. Eliminate further redundancy by allowing the drvname argument to DEFINE_XENBUS_DRIVER() to be blank (in which case the first entry from the ID table will be used for .driver.name). Also eliminate the questionable xenbus_register_{back,front}end() wrappers - their sole remaining purpose was the checking of the 'owner' field, proper setting of which shouldn't be an issue anymore when the macro gets used. v2: Restore DRV_NAME for the driver name in xen-pciback. Signed-off-by: Jan Beulich <jbeulich@suse.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de> Cc: Ian Campbell <ian.campbell@citrix.com> Cc: David S. Miller <davem@davemloft.net> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-12-02treewide: Fix typos in various parts of the kernel, and fix some comments.Justin P. Mattock
The below patch fixes some typos in various parts of the kernel, as well as fixes some comments. Please let me know if I missed anything, and I will try to get it changed and resent. Signed-off-by: Justin P. Mattock <justinmattock@gmail.com> Acked-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-11-06Merge branch 'stable/vmalloc-3.2' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen * 'stable/vmalloc-3.2' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen: net: xen-netback: use API provided by xenbus module to map rings block: xen-blkback: use API provided by xenbus module to map rings xen: use generic functions instead of xen_{alloc, free}_vm_area()
2011-11-04Merge branch 'for-3.2/drivers' of git://git.kernel.dk/linux-blockLinus Torvalds
* 'for-3.2/drivers' of git://git.kernel.dk/linux-block: (30 commits) virtio-blk: use ida to allocate disk index hpsa: add small delay when using PCI Power Management to reset for kump cciss: add small delay when using PCI Power Management to reset for kump xen/blkback: Fix two races in the handling of barrier requests. xen/blkback: Check for proper operation. xen/blkback: Fix the inhibition to map pages when discarding sector ranges. xen/blkback: Report VBD_WSECT (wr_sect) properly. xen/blkback: Support 'feature-barrier' aka old-style BARRIER requests. xen-blkfront: plug device number leak in xlblk_init() error path xen-blkfront: If no barrier or flush is supported, use invalid operation. xen-blkback: use kzalloc() in favor of kmalloc()+memset() xen-blkback: fixed indentation and comments xen-blkfront: fix a deadlock while handling discard response xen-blkfront: Handle discard requests. xen-blkback: Implement discard requests ('feature-discard') xen-blkfront: add BLKIF_OP_DISCARD and discard request struct drivers/block/loop.c: remove unnecessary bdev argument from loop_clr_fd() drivers/block/loop.c: emit uevent on auto release drivers/block/cpqarray.c: use pci_dev->revision loop: always allow userspace partitions and optionally support automatic scanning ... Fic up trivial header file includsion conflict in drivers/block/loop.c
2011-10-26block: xen-blkback: use API provided by xenbus module to map ringsDavid Vrabel
The xenbus module provides xenbus_map_ring_valloc() and xenbus_map_ring_vfree(). Use these to map the ring pages granted by the frontend. Acked-by: Jens Axboe <jaxboe@fusionio.com> Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-25Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial: (59 commits) MAINTAINERS: linux-m32r is moderated for non-subscribers linux@lists.openrisc.net is moderated for non-subscribers Drop default from "DM365 codec select" choice parisc: Kconfig: cleanup Kernel page size default Kconfig: remove redundant CONFIG_ prefix on two symbols cris: remove arch/cris/arch-v32/lib/nand_init.S microblaze: add missing CONFIG_ prefixes h8300: drop puzzling Kconfig dependencies MAINTAINERS: microblaze-uclinux@itee.uq.edu.au is moderated for non-subscribers tty: drop superfluous dependency in Kconfig ARM: mxc: fix Kconfig typo 'i.MX51' Fix file references in Kconfig files aic7xxx: fix Kconfig references to READMEs Fix file references in drivers/ide/ thinkpad_acpi: Fix printk typo 'bluestooth' bcmring: drop commented out line in Kconfig btmrvl_sdio: fix typo 'btmrvl_sdio_sd6888' doc: raw1394: Trivial typo fix CIFS: Don't free volume_info->UNC until we are entirely done with it. treewide: Correct spelling of successfully in comments ...
2011-10-25Merge branches 'stable/bug.fixes-3.2' and 'stable/mmu.fixes' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen * 'stable/bug.fixes-3.2' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen: xen/p2m/debugfs: Make type_name more obvious. xen/p2m/debugfs: Fix potential pointer exception. xen/enlighten: Fix compile warnings and set cx to known value. xen/xenbus: Remove the unnecessary check. xen/irq: If we fail during msi_capability_init return proper error code. xen/events: Don't check the info for NULL as it is already done. xen/events: BUG() when we can't allocate our event->irq array. * 'stable/mmu.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen: xen: Fix selfballooning and ensure it doesn't go too far xen/gntdev: Fix sleep-inside-spinlock xen: modify kernel mappings corresponding to granted pages xen: add an "highmem" parameter to alloc_xenballooned_pages xen/p2m: Use SetPagePrivate and its friends for M2P overrides. xen/p2m: Make debug/xen/mmu/p2m visible again. Revert "xen/debug: WARN_ON when identity PFN has no _PAGE_IOMAP flag set."
2011-10-17xen/blkback: Fix two races in the handling of barrier requests.Konrad Rzeszutek Wilk
There are two windows of opportunity to cause a race when processing a barrier request. This patch fixes this. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-14xen/blkback: Check for proper operation.Konrad Rzeszutek Wilk
The patch titled: "xen/blkback: Fix the inhibition to map pages when discarding sector ranges." had the right idea except that it used the wrong comparison operator. It had == instead of !=. This fixes the bug where all (except discard) operations would have been ignored. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-13xen/blkback: Fix the inhibition to map pages when discarding sector ranges.Konrad Rzeszutek Wilk
The 'operation' parameters are the ones provided to the bio layer while the req->operation are the ones passed in between the backend and frontend. We used the wrong 'operation' value to squash the call to map pages when processing the discard operation resulting in an hypercall that did nothing. Lets guard against going in the mapping function by checking for the proper operation type. CC: Li Dongyang <lidongyang@novell.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-13xen/blkback: Report VBD_WSECT (wr_sect) properly.Konrad Rzeszutek Wilk
We did not increment the amount of sectors written to disk b/c we tested for the == WRITE which is incorrect - as the operations are more of WRITE_FLUSH, WRITE_ODIRECT. This patch fixes it by doing a & WRITE check. CC: stable@kernel.org Reported-by: Andy Burns <xen.lists@burns.me.uk> Suggested-by: Ian Campbell <Ian.Campbell@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-13xen/blkback: Support 'feature-barrier' aka old-style BARRIER requests.Konrad Rzeszutek Wilk
We emulate the barrier requests by draining the outstanding bio's and then sending the WRITE_FLUSH command. To drain the I/Os we use the refcnt that is used during disconnect to wait for all the I/Os before disconnecting from the frontend. We latch on its value and if it reaches either the threshold for disconnect or when there are no more outstanding I/Os, then we have drained all I/Os. Suggested-by: Christopher Hellwig <hch@infradead.org> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-13xen-blkback: use kzalloc() in favor of kmalloc()+memset()Jan Beulich
This fixes the problem of three of those four memset()-s having improper size arguments passed: Sizeof a pointer-typed expression returns the size of the pointer, not that of the pointed to data. It also reverts using kmalloc() instead of kzalloc() for the allocation of the pending grant handles array, as that array gets fully initialized in a subsequent loop. Reported-by: Julia Lawall <julia@diku.dk> Signed-off-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-13xen-blkback: fixed indentation and commentsJoe Jin
This patch fixes belows: 1. Fix code style issue. 2. Fix incorrect functions name in comments. Signed-off-by: Joe Jin <joe.jin@oracle.com> Cc: Jens Axboe <jaxboe@fusionio.com> Cc: Ian Campbell <Ian.Campbell@eu.citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-10-13xen-blkback: Implement discard requests ('feature-discard')Li Dongyang
..aka ATA TRIM/SCSI UNMAP command to be passed through the frontend and used as appropiately by the backend. We also advertise certain granulity parameters to the frontend so it can plug them in. If the backend is a realy device - we just end up using 'blkdev_issue_discard' while for loopback devices - we just punch a hole in the image file. Signed-off-by: Li Dongyang <lidongyang@novell.com> [v1: Fixed up pr_debug and commit description] Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-09-29xen: modify kernel mappings corresponding to granted pagesStefano Stabellini
If we want to use granted pages for AIO, changing the mappings of a user vma and the corresponding p2m is not enough, we also need to update the kernel mappings accordingly. Currently this is only needed for pages that are created for user usages through /dev/xen/gntdev. As in, pages that have been in use by the kernel and use the P2M will not need this special mapping. However there are no guarantees that in the future the kernel won't start accessing pages through the 1:1 even for internal usage. In order to avoid the complexity of dealing with highmem, we allocated the pages lowmem. We issue a HYPERVISOR_grant_table_op right away in m2p_add_override and we remove the mappings using another HYPERVISOR_grant_table_op in m2p_remove_override. Considering that m2p_add_override and m2p_remove_override are called once per page we use multicalls and hypercall batching. Use the kmap_op pointer directly as argument to do the mapping as it is guaranteed to be present up until the unmapping is done. Before issuing any unmapping multicalls, we need to make sure that the mapping has already being done, because we need the kmap->handle to be set correctly. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> [v1: Removed GRANT_FRAME_BIT usage] Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-09-15Remove unneeded version.h includes from drivers/block/Jesper Juhl
It was pointed out by 'make versioncheck' that some includes of linux/version.h are not needed in drivers/block/. This patch removes them. Signed-off-by: Jesper Juhl <jj@chaosbits.net> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-08-23Merge branch 'stable/for-jens' of ↵Jens Axboe
git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen into for-linus
2011-08-22xen-blkback: fixed indentation and commentsJoe Jin
This patch fixes belows: 1. Fix code style issue. 2. Fix incorrect functions name in comments. Signed-off-by: Joe Jin <joe.jin@oracle.com> Cc: Jens Axboe <jaxboe@fusionio.com> Cc: Ian Campbell <Ian.Campbell@eu.citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-08-22xen-blkback: Don't disconnect backend until state switched to XenbusStateClosed.Joe Jin
When do block-attach/block-detach test with below steps, umount hangs in the guest. Furthermore shutdown ends up being stuck when umounting file-systems. 1. start guest. 2. attach new block device by xm block-attach in Dom0. 3. mount new disk in guest. 4. execute xm block-detach to detach the block device in dom0 until timeout 5. Any request to the disk will hung. Root cause: This issue is caused when setting backend device's state to 'XenbusStateClosing', which sends to the frontend the XenbusStateClosing notification. When frontend receives the notification it tries to release the disk in blkfront_closing(), but at that moment the disk is still in use by guest, so frontend refuses to close. Specifically it sets the disk state to XenbusStateClosing and sends the notification to backend - when backend receives the event, it disconnects the vbd from real device, and sets the vbd device state to XenbusStateClosing. The backend disconnects the real device/file, and any IO requests to the disk in guest will end up in ether, leaving disk DEAD and set to XenbusStateClosing. When the guest wants to disconnect the disk, umount will hang on blkif_release()->xlvbd_release_gendisk() as it is unable to send any IO to the disk, which prevents clean system shutdown. Solution: Don't disconnect backend until frontend state switched to XenbusStateClosed. Signed-off-by: Joe Jin <joe.jin@oracle.com> Cc: Daniel Stodden <daniel.stodden@citrix.com> Cc: Jens Axboe <jaxboe@fusionio.com> Cc: Annie Li <annie.li@oracle.com> Cc: Ian Campbell <Ian.Campbell@eu.citrix.com> [v1: Modified description a bit] Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-07-25Merge branch 'for-3.1/drivers' of git://git.kernel.dk/linux-blockLinus Torvalds
* 'for-3.1/drivers' of git://git.kernel.dk/linux-block: cciss: do not attempt to read from a write-only register xen/blkback: Add module alias for autoloading xen/blkback: Don't let in-flight requests defer pending ones. bsg: fix address space warning from sparse bsg: remove unnecessary conditional expressions bsg: fix bsg_poll() to return POLLOUT properly
2011-06-30xen/blkback: Add module alias for autoloadingBastian Blank
Add xen-backend:vbd module alias to the xen-blkback module. This allows automatic loading of the module. Signed-off-by: Bastian Blank <waldi@debian.org> Acked-by: Ian Campbell <ian.campbell@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-06-30xen/blkback: Don't let in-flight requests defer pending ones.Daniel Stodden
Running RING_FINAL_CHECK_FOR_REQUESTS from make_response is a bad idea. It means that in-flight I/O is essentially blocking continued batches. This essentially kills throughput on frontends which unplug (or even just notify) early and rightfully assume addtional requests will be picked up on time, not synchronously. Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com> [v1: Rebased and fixed compile problems] Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-06-30xen: Add __attribute__((format(printf... where appropriateJoe Perches
Use the compiler to verify printf formats and arguments. Fix fallout. Signed-off-by: Joe Perches <joe@perches.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-06-01xen/blkback: potential null dereference in error handlingDan Carpenter
blkbk->pending_pages can be NULL here so I added a check for it. Signed-off-by: Dan Carpenter <error27@gmail.com> [v1: Redid the loop a bit] Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-06-01xen/blkback: don't call vbd_size() if bd_disk is NULLLaszlo Ersek
...because vbd_size() dereferences bd_disk if bd_part is NULL. Signed-off-by: Laszlo Ersek<lersek@redhat.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-18xen/blkback: don't fail empty barrier requestsJan Beulich
The sector number on empty barrier requests may (will?) be -1, which, given that it's being treated as unsigned 64-bit quantity, will almost always exceed the actual (virtual) disk's size. Inspired by Konrad's "When writting barriers set the sector number to zero...". While at it also add overflow checking to the math in vbd_translate(). Signed-off-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-13xen/blkback: fix xenbus_transaction_start() hang caused by double ↵Laszlo Ersek
xenbus_transaction_end() vbd_resize() up_read()'s xs_state.suspend_mutex twice in a row via double xenbus_transaction_end() calls. The next down_read() in xenbus_transaction_start() (at eg. the next resize attempt) hangs. Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=618317 Acked-by: Jan Beulich <jbeulich@novell.com> Acked-by: Ian Campbell <ian.campbell@citrix.com> Signed-off-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Align the tabs on the structure.Konrad Rzeszutek Wilk
The recent changes caused this field of the structure to be offset a bit. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: if log_stats is enabled print out the data.Konrad Rzeszutek Wilk
And not depend on the driver being built with -DDEBUG flag. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Add the prefix XEN in the common.h.Konrad Rzeszutek Wilk
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Prefix 'vbd' with 'xen' in structs and functions.Konrad Rzeszutek Wilk
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Change structure name blkif_st to xen_blkif.Konrad Rzeszutek Wilk
No need for that '_st' and xen_blkif is more apt. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Remove the unused typedefs.Konrad Rzeszutek Wilk
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Move include/xen/blkif.h into drivers/block/xen-blkback/common.hKonrad Rzeszutek Wilk
Not point of the blkif.h file. It is not used by the frontend. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Fixing some more of the cleanpatch.pl warnings.Konrad Rzeszutek Wilk
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Checkpatch.pl recommend against multiple assigments.Konrad Rzeszutek Wilk
CHECK: multiple assignments should be avoided Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Fix spelling mistakes.Konrad Rzeszutek Wilk
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Move blkif_get_x86_[32|64]_req to common.h in block/xen-blkback ↵Konrad Rzeszutek Wilk
dir. From the blkif.h header, which was exposed to the frontend. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Removing the debug_lvl option.Konrad Rzeszutek Wilk
It is not really used for anything. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Use the DRV_PFX in the pr_.. macros.Konrad Rzeszutek Wilk
To make it easier to read. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Make the DPRINTK uniform.Konrad Rzeszutek Wilk
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-12xen/blkback: Change printk/DPRINTK to pr_.. type variant.Konrad Rzeszutek Wilk
And also make them uniform and prefix the message with 'xen-blkback'. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-11xen/blkback: Fixed up comments and converted spaces to tabs.Konrad Rzeszutek Wilk
Suggested-by: Ian Campbell <Ian.Campbell@eu.citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-05xen/blkback: Fix up some of the comments.Konrad Rzeszutek Wilk
They had the wrong data or were in the wrong spot. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-05xen/blkback: Squash the checking for operation into dispatch_rw_block_ioKonrad Rzeszutek Wilk
We do a check for the operations right before calling dispatch_rw_block_io. And then we do the same check in dispatch_rw_block_io. This patch squashes those checks into the 'dispatch_rw_block_io' function. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-05-05xen/blkback: Add support for BLKIF_OP_FLUSH_DISKCACHE and drop ↵Konrad Rzeszutek Wilk
BLKIF_OP_WRITE_BARRIER. We drop the support for 'feature-barrier' and add in the support for the 'feature-flush-cache' if the real backend storage supports flushing. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
2011-04-27Revert "xen/blkback: Move the plugging/unplugging to a higher level."Konrad Rzeszutek Wilk
This reverts commit 97961ef46b9b5a6a7c918a38b898a7b3e49869f4 b/c we lose about 15% performance if we do the unplugging and the end of the reading the ring buffer.
2011-04-26xen/blkback: Stick REQ_SYNC on WRITEs to deal with CFQ I/O scheduler.Konrad Rzeszutek Wilk
If one runs a simple fio request with random read/write with a 20%/80% ratio, the numbers are incredibly bad when using the CFQ scheduler. IOmeter | | | | 64K, randrw | NOOP | CFQ | deadline | randrwmix=80 | | | | --------------+-------+------+----------+ blkback |103/27 |32/10 | 102/27 | --------------+-------+------+----------+ QEMU qdisk |103/27 |102/27| 102/27 | The problem as explained by Vivek Goyal was: ".. that difference is that sync vs async requests. In the case of a kernel thread submitting IO, [..] all the WRITES might be being considered as async and will go in a different queue. If you mix those with some READS, they are always sync and will go in differnet queue. In presence of sync queue, CFQ will idle and choke up WRITES in an attempt to improve latencies of READs. In case of AIO [note: this is what QEMU qdisk is doing] , [..] it is direct IO and both READS and WRITES will be considered SYNC and will go in a single queue and no choking of WRITES will take place." The solution is quite simple, tack on REQ_SYNC (which is what the WRITE_ODIRECT macro points to) and the numbers go back up. Suggested-by: Vivek Goyal <vgoyal@redhat.com Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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