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From: | Alexey Perevalov |
Subject: | Re: [Qemu-devel] [PATCH v12 1/6] migration: introduce postcopy-blocktime capability |
Date: | Fri, 05 Jan 2018 15:10:03 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 |
On 01/03/2018 12:20 AM, Eric Blake wrote:
On 10/30/2017 08:16 AM, Alexey Perevalov wrote:Right now it could be used on destination side to enable vCPU blocktime calculation for postcopy live migration. vCPU blocktime - it's time since vCPU thread was put into interruptible sleep, till memory page was copied and thread awake. Reviewed-by: Dr. David Alan Gilbert <address@hidden> Signed-off-by: Alexey Perevalov <address@hidden> --- migration/migration.c | 9 +++++++++ migration/migration.h | 1 + qapi/migration.json | 6 +++++- 3 files changed, 15 insertions(+), 1 deletion(-)Is there any reason this has to be a new capability rather than unconditionally enabled? What are the trade-offs for enabling vs. disabling the capability that warrant it being a knob? Can we do a better job of documenting in which cases the user would want to change the knob from its default value, if we even need it to be a knob?
Hello Eric, sorry for late response, it's holiday in whole Russia. The reason we decided to introduce new capability it's performance penalty, memory & cpu usage, in current versionit's not so high as in initial, it affects hot path of post-copy live migration.
Regarding documentation part, I'll answer in "[PATCH v12 6/6] migration: add postcopy total blocktime into query-migrate" thread.
+++ b/qapi/migration.json @@ -352,12 +352,16 @@ # # @x-multifd: Use more than one fd for migration (since 2.11) # +# @postcopy-blocktime: Calculate downtime for postcopy live migration +# (since 2.11) +# # Since: 1.2 ## { 'enum': 'MigrationCapability', 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks', 'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram', - 'block', 'return-path', 'pause-before-switchover', 'x-multifd' ] } + 'block', 'return-path', 'pause-before-switchover', 'x-multifd', + 'postcopy-blocktime' ] }### @MigrationCapabilityStatus:
-- Best regards, Alexey Perevalov
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