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doc/nvme: describe fused operations support

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Change-Id: Ifcc2bf59051d5cee261cfc4898e267ed7608c1a8
Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
Signed-off-by: Maciej Szwed <maciej.szwed@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/477789
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
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Maciej Szwed 2020-01-23 11:24:46 +01:00 committed by Tomasz Zawadzki
parent a83644fe2b
commit ca07f62b5b
1 changed files with 32 additions and 0 deletions
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doc/nvme.md
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@ -117,6 +117,38 @@ spdk_nvme_qpair_process_completions().
@sa spdk_nvme_ns_cmd_read, spdk_nvme_ns_cmd_write, spdk_nvme_ns_cmd_dataset_management,
spdk_nvme_ns_cmd_flush, spdk_nvme_qpair_process_completions
### Fused operations {#nvme_fuses}
To "fuse" two commands, the first command should have the SPDK_NVME_IO_FLAGS_FUSE_FIRST
io flag set, and the next one should have the SPDK_NVME_IO_FLAGS_FUSE_SECOND.
In addition, the following rules must be met to execute two commands as an atomic unit:
- The commands shall be inserted next to each other in the same submission queue.
- The LBA range, should be the same for the two commands.
E.g. To send fused compare and write operation user must call spdk_nvme_ns_cmd_compare
followed with spdk_nvme_ns_cmd_write and make sure no other operations are submitted
in between on the same queue, like in example below:
~~~
rc = spdk_nvme_ns_cmd_compare(ns, qpair, cmp_buf, 0, 1, nvme_fused_first_cpl_cb,
NULL, SPDK_NVME_CMD_FUSE_FIRST);
if (rc != 0) {
...
}
rc = spdk_nvme_ns_cmd_write(ns, qpair, write_buf, 0, 1, nvme_fused_second_cpl_cb,
NULL, SPDK_NVME_CMD_FUSE_SECOND);
if (rc != 0) {
...
}
~~~
The NVMe specification currently defines compare-and-write as a fused operation.
Support for compare-and-write is reported by the controller flag
SPDK_NVME_CTRLR_COMPARE_AND_WRITE_SUPPORTED.
### Scaling Performance {#nvme_scaling}
NVMe queue pairs (struct spdk_nvme_qpair) provide parallel submission paths for