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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] migration: adding migration to/from a file (v2) |
Date: | Thu, 19 Feb 2009 14:06:41 -0600 |
User-agent: | Thunderbird 2.0.0.19 (X11/20090105) |
Jamie Lokier wrote:
Remember, migration is a streaming protocol, not a random access, so it only makes sense to have one outstanding request at a time.Fwow, often with streaming (in general) the highest performance comes from having two or more outstanding requests at a time, so there are no gaps between requests being processed at the OS and device level. However, unless migrate-to-file uses O_DIRECT that will be hidden by the OS's buffering.
It's already buffered FWIW by the savevm infrastructure. You'll won't usually see small operations.
Regards, Anthony Liguori
Then the remaining overhead from AIOs (or fake AIOs using threads) is lots context switching, one per write completed. -- Jamie
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