[RFC,1/4] Curling: add doc

Message ID 1378784607-7398-2-git-send-email-junqing.wang@cs2c.com.cn
State New
Headers show

Commit Message

Jules Wang Sept. 10, 2013, 3:43 a.m.
Curling provides fault tolerant mechanism for KVM.
For more info, see 'doc/curling.txt'.

Signed-off-by: Jules Wang <junqing.wang@cs2c.com.cn>
 docs/curling.txt | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 docs/curling.txt


diff --git a/docs/curling.txt b/docs/curling.txt
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+KVM Fault Tolerance Specification
+* Introduction
+* Usage
+* Design & Implement
+* Performance
+The goal of Curling(sports) is to provide a fault tolerant(ft for short)
+mechanism for KVM, so that in the event of a hardware failure, the virtual
+machine fails over to the backup in a way that is completely transparent
+to the guest operating system.
+The steps of curling are the same as the steps of live migration except the
+1. Start the receiver vm with -incoming curling:tcp:<address>:<port>
+2. Start ft in the qemu monitor of sender vm by following cmdline:
+   > migrate_set_speed <full bandwidth>
+   > migrate curling:tcp:<address>:<port>
+3. Connect to the receiver vm by vnc or spice. The screen of the vm is displayed
+when curling is ready.
+4. Now, the sender vm is protected by ft, When it encounters a failure,
+the failover kicks in.
+Design & Implement
+* By leveraging live migration feature, we do endless live migrations between
+the sender and receiver, so the two virtual machines are synchronized.
+* The receiver does not load vm state once the migration begins, instead, it
+perfetches one whole migration data into a buffer, then loads vm state from
+that buffer afterwards. This "all or nothing" approach prevents the
+broken-in-the-middle problem Kemari has.
+* The sender sleeps a little while after each migration, to ease the
+performance penalty entailed by vm_stop and iothread locks. This is a
+tradeoff between performance and accuracy.