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6cc5683390
The minimal size of request in the block framework is always PAGE_SIZE. It means that when 64KB guest is support, the request will at least be 64KB. Although, if the backend doesn't support indirect descriptor (such as QDISK in QEMU), a ring request is only able to accommodate 11 segments of 4KB (i.e 44KB). The current frontend is assuming that an I/O request will always fit in a ring request. This is not true any more when using 64KB page granularity and will therefore crash during boot. On ARM64, the ABI is completely neutral to the page granularity used by the domU. The guest has the choice between different page granularity supported by the processors (for instance on ARM64: 4KB, 16KB, 64KB). This can't be enforced by the hypervisor and therefore it's possible to run guests using different page granularity. So we can't mandate the block backend to support indirect descriptor when the frontend is using 64KB page granularity and have to fix it properly in the frontend. The solution exposed below is based on modifying directly the frontend guest rather than asking the block framework to support smaller size (i.e < PAGE_SIZE). This is because the change is the block framework are not trivial as everything seems to relying on a struct *page (see [1]). Although, it may be possible that someone succeed to do it in the future and we would therefore be able to use it. Given that a block request may not fit in a single ring request, a second request is introduced for the data that cannot fit in the first one. This means that the second ring request should never be used on Linux if the page size is smaller than 44KB. To achieve the support of the extra ring request, the block queue size is divided by two. Therefore, the ring will always contain enough space to accommodate 2 ring requests. While this will reduce the overall performance, it will make the implementation more contained. The way forward to get better performance is to implement in the backend either indirect descriptor or multiple grants ring. Note that the parameters blk_queue_max_* helpers haven't been updated. The block code will set the mimimum size supported and we may be able to support directly any change in the block framework that lower down the minimal size of a request. [1] http://lists.xen.org/archives/html/xen-devel/2015-08/msg02200.html Signed-off-by: Julien Grall <julien.grall@citrix.com> Acked-by: Roger Pau Monné <roger.pau@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> |
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| aoe | ||
| drbd | ||
| mtip32xx | ||
| paride | ||
| rsxx | ||
| xen-blkback | ||
| zram | ||
| amiflop.c | ||
| ataflop.c | ||
| brd.c | ||
| cciss.c | ||
| cciss.h | ||
| cciss_cmd.h | ||
| cciss_scsi.c | ||
| cciss_scsi.h | ||
| cpqarray.c | ||
| cpqarray.h | ||
| cryptoloop.c | ||
| DAC960.c | ||
| DAC960.h | ||
| floppy.c | ||
| hd.c | ||
| ida_cmd.h | ||
| ida_ioctl.h | ||
| Kconfig | ||
| loop.c | ||
| loop.h | ||
| Makefile | ||
| mg_disk.c | ||
| nbd.c | ||
| null_blk.c | ||
| osdblk.c | ||
| pktcdvd.c | ||
| ps3disk.c | ||
| ps3vram.c | ||
| rbd.c | ||
| rbd_types.h | ||
| skd_main.c | ||
| skd_s1120.h | ||
| smart1,2.h | ||
| sunvdc.c | ||
| swim.c | ||
| swim3.c | ||
| swim_asm.S | ||
| sx8.c | ||
| umem.c | ||
| umem.h | ||
| virtio_blk.c | ||
| xen-blkfront.c | ||
| xsysace.c | ||
| z2ram.c | ||