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DescriptionLuiz Capitulino
2017-05-18 18:28:05 UTC
Description of problem:
The realtime-virtual-guest profile doesn't allow for running a PMD thread with fifo:1 priority in the guest. This is so because the profile doesn't organizes CPU bound kernel threads into FIFO slots as done by the realtime-virtual-host profile.
This is how the realtime-virtual-host profile organizes kernel threads into FIFO slots:
151 FF 4 [rcuc/15] *
153 FF 3 [ktimersoftd/15] *
154 FF 2 [ksoftirqd/15] *
As we can see, rcuc > ktimersoftd > ksoftirqd. This allows for running a PMD thread with fifo:1 without running into the risk of starving those important threads.
However, the realtime-virtual-guest doesn't do any of this:
17 FF 2 [rcuc/1] *
19 FF 1 [ktimersoftd/1] *
20 TS - [ksoftirqd/1] *
So, a PMD thread running in the guest with fifo:1 can starve ktimersoftd and ksoftirqd should those threads ever become runnable.
The solution should be the realtime-virtual-guest profile to assign FIFO priority to kernel threads the same way the realtime-virtual-host is doing.
Version-Release number of selected component (if applicable): tuned-2.8.0-3.el7.noarch
Comment 2Jaroslav Škarvada
2017-05-29 15:42:57 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2017:2102
Comment 16Fedora Update System
2017-10-13 14:20:34 UTC
Description of problem: The realtime-virtual-guest profile doesn't allow for running a PMD thread with fifo:1 priority in the guest. This is so because the profile doesn't organizes CPU bound kernel threads into FIFO slots as done by the realtime-virtual-host profile. This is how the realtime-virtual-host profile organizes kernel threads into FIFO slots: 151 FF 4 [rcuc/15] * 153 FF 3 [ktimersoftd/15] * 154 FF 2 [ksoftirqd/15] * As we can see, rcuc > ktimersoftd > ksoftirqd. This allows for running a PMD thread with fifo:1 without running into the risk of starving those important threads. However, the realtime-virtual-guest doesn't do any of this: 17 FF 2 [rcuc/1] * 19 FF 1 [ktimersoftd/1] * 20 TS - [ksoftirqd/1] * So, a PMD thread running in the guest with fifo:1 can starve ktimersoftd and ksoftirqd should those threads ever become runnable. The solution should be the realtime-virtual-guest profile to assign FIFO priority to kernel threads the same way the realtime-virtual-host is doing. Version-Release number of selected component (if applicable): tuned-2.8.0-3.el7.noarch