Costa: Designing a Userspace Disk I/O Scheduler for Modern Datastores: the Scylla example (Part 1)

Posted Apr 19, 2016 6:26 UTC (Tue) by joib (subscriber, #8541)
In reply to: Costa: Designing a Userspace Disk I/O Scheduler for Modern Datastores: the Scylla example (Part 1) by jospoortvliet
Parent article: Costa: Designing a Userspace Disk I/O Scheduler for Modern Datastores: the Scylla example (Part 1)

Well, they want to do async block I/O, which means they must use the (Linux-specific) io_submit interface, which implies they use O_DIRECT, page-aligned I/O etc. So it's not adding yet another layer on top of the kernel as much as replacing the kernel stuff with their own I/O scheduler, page cache etc.

Costa: Designing a Userspace Disk I/O Scheduler for Modern Datastores: the Scylla example (Part 1)

Posted Apr 19, 2016 12:01 UTC (Tue) by rnsanchez (guest, #32570) [Link] (1 responses)

You still have the kernel's page cache if you make your own userspace I/O scheduler, which is a tremendous help if the page cache is not the problem you're trying to solve.

Costa: Designing a Userspace Disk I/O Scheduler for Modern Datastores: the Scylla example (Part 1)

Posted Apr 19, 2016 16:26 UTC (Tue) by mtanski (guest, #56423) [Link]

But without O_DIRECT and io_submit you lose async behavior of read/write which many people care about.