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as before. The common scheduling bits have moved from inline code in each of the CAM periph drivers into a library that implements the default scheduling. In addition, a number of rate-limiting and I/O preference options can be enabled by adding CAM_IOSCHED_NETFLIX to your config file. A number of extra stats are also maintained. CAM_IOSCHED_NETFLIX isn't on by default because it uses a separate BIO_READ and BIO_WRITE queue, so doesn't honor BIO_ORDERED between these two types of operations. We already didn't honor it for BIO_DELETE, and we don't depend on BIO_ORDERED between reads and writes anywhere in the system (it is currently used with BIO_FLUSH in ZFS to make sure some writes are complete before others start and as a poor-man's soft dependency in one place in UFS where we won't be issuing READs until after the operation completes). However, out of an abundance of caution, it isn't enabled by default. Plus, this also brings in NCQ TRIM support for those SSDs that support it. A black list is also provided for known rogues that use NCQ trim as an excuse to corrupt the drive. It was difficult to separate out into a separate commit. This code has run in production at Netflix for over a year now. Sponsored by: Netflix, Inc Differential Revision: https://reviews.freebsd.org/D4609
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