a8b2e30685
When sequential scrubs were merged, all calls to arc_read() (including prefetch IOs) were given ZIO_PRIORITY_ASYNC_READ. Unfortunately, this behaves badly with an existing issue where prefetch IOs cannot be re-prioritized after the issue. The result is that synchronous reads end up in the same vdev_queue as the scrub IOs and can have (in some workloads) multiple seconds of latency. This patch incorporates 2 changes. The first ensures that all scrub IOs are given ZIO_PRIORITY_SCRUB to allow the vdev_queue code to differentiate between these I/Os and user prefetches. Second, this patch introduces zio_change_priority() to provide the missing capability to upgrade a zio's priority. Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Tom Caputi <tcaputi@datto.com> Closes #6921 Closes #6926 |
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