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aaebf69062
the blkfront driver to perform I/Os of up to 2 MB, subject to support from the blkback to which it is connected and the initiation of such large I/Os by the rest of the kernel. In practice, the I/O size is increased from 40 kB to 128 kB. The changes to xen/interface/io/blkif.h consist merely of merging updates from the upstream Xen repository. In dev/xen/blkfront/block.h we add some convenience macros and structure fields used for indirect-page I/Os: The device records its negotiated limit on the number of indirect pages used, while each I/O command structure gains permanently allocated page(s) for indirect page references and the Xen grant references for those pages. In dev/xen/blkfront/blkfront.c we now check in xbd_queue_cb whether a request is small enough to handle without an indirection page, and either follow the previous behaviour or use new code for issuing an indirect segment I/O. In xbd_connect we read the size of indirect segment I/Os supported by the backend and select the maximum size we will use; then allocate the pages and Xen grant references for each I/O command structure. In xbd_free those grants and pages are released. A new loader tunable, hw.xbd.xbd_enable_indirect, can be set to 0 in order to disable this functionality; it works by pretending that the backend does not support this feature. Some backends exhibit a loss of performance with large I/Os, so users may wish to test with and without this functionality enabled. Reviewed by: royger MFC after: 3 days Relnotes: yes |
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| .. | ||
| balloon | ||
| blkback | ||
| blkfront | ||
| console | ||
| control | ||
| debug | ||
| evtchn | ||
| grant_table | ||
| netback | ||
| netfront | ||
| pci | ||
| pcifront | ||
| privcmd | ||
| pvcpu | ||
| timer | ||
| xenpci | ||
| xenstore | ||