Bug 1240494
| Summary: | The system won't bypass the cache even enable the auto_dump_bypass_cache in qemu.conf | ||||||
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| Product: | Red Hat Enterprise Linux 7 | Reporter: | Dan Zheng <dzheng> | ||||
| Component: | libvirt | Assignee: | Andrea Bolognani <abologna> | ||||
| Status: | CLOSED NOTABUG | QA Contact: | Virtualization Bugs <virt-bugs> | ||||
| Severity: | medium | Docs Contact: | |||||
| Priority: | medium | ||||||
| Version: | 7.2 | CC: | abologna, dyuan, gsun, lhuang, mzhan, ngu, rbalakri | ||||
| Target Milestone: | rc | ||||||
| Target Release: | --- | ||||||
| Hardware: | ppc64le | ||||||
| OS: | Linux | ||||||
| Whiteboard: | |||||||
| Fixed In Version: | Doc Type: | If docs needed, set a value | |||||
| Doc Text: | Story Points: | --- | |||||
| Clone Of: | Environment: | ||||||
| Last Closed: | 2017-04-07 10:42:14 UTC | Type: | Bug | ||||
| Regression: | --- | Mount Type: | --- | ||||
| Documentation: | --- | CRM: | |||||
| Verified Versions: | Category: | --- | |||||
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||
| Cloudforms Team: | --- | Target Upstream Version: | |||||
| Embargoed: | |||||||
| Attachments: |
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Created attachment 1269673 [details]
Program showing the effect of O_DIRECT on /proc/*/fdinfo/*
(In reply to Dan Zheng from comment #0) [...] > # cat /proc/$(lsof -w /var/lib/libvirt/qemu/dump/*|awk '/libvirt_i/{print > $2}')/fdinfo/*1* > pos: 3822059520 > flags: 0600001 > ... > pos: 3968860160 > flags: 0600001 > ... > pos: 4107272192 > flags: 0600001 > > Actual result: > In the flags in step 6 output, the third value is '0' which stands for > 'auto_dump_bypass_cache' is disabled. The system did not bypass the cache > for auto dump with auto_dump_bypass_cache enabled. > > Expect result: > In the flags in step 6 output, the third value is '4' which stands for > 'auto_dump_bypass_cache' is enabled. The system should bypass the cache for > auto dump with auto_dump_bypass_cache enabled. The testing methodology is not entirely correct because it doesn't account for the fact that the concrete value for eg. O_DIRECT can be different depending on the architecture. I've attached a simple C program that demostrates the issue: when run on an x86_64 host, it will print $ ./direct whatever Without O_DIRECT: pos: 0 flags: 0100001 mnt_id: 62 With O_DIRECT: pos: 0 flags: 0140001 mnt_id: 62 whereas on a ppc64le or aarch64 host it will print $ ./direct whatever Without O_DIRECT: pos: 0 flags: 0400001 mnt_id: 80 With O_DIRECT: pos: 0 flags: 0600001 mnt_id: 80 So 0600001 is the expected output for ppc64le hosts, and libvirt is behaving correctly. Closing as NOTABUG. |
Description of problem: The system won't bypass the cache even enable the auto_dump_bypass_cache in qemu.conf. This problem does not exist on x86. Version-Release number of selected component (if applicable): libvirt-1.2.17-1.el7.ppc64le qemu-kvm-rhev-2.3.0-5.el7.ppc64le kernel-3.10.0-282.el7.ppc64le How reproducible: 100% Steps to Reproduce: 1. Set auto_dump_bypass_cache = 1 in qemu.conf # cat /etc/libvirt/qemu.conf ... auto_dump_bypass_cache = 1 ... 2. Restart libvirtd, # systemctl restart libvirtd 3. Edit XML with <on_crash>coredump-restart</on_crash> 4. Start guest. 5. Prepare command line on another terminal-2 with below command. # cat /proc/$(lsof -w /var/lib/libvirt/qemu/dump/*|awk '/libvirt_i/{print $2}')/fdinfo/*1* 6. Within the guest, stop kdump service and make the guest crash. # systemctl stop kdump # echo c > /proc/sysrq-trigger 7. Before the guest finishes crashing, run the command on step 5 for many times on terminal-2 # cat /proc/$(lsof -w /var/lib/libvirt/qemu/dump/*|awk '/libvirt_i/{print $2}')/fdinfo/*1* pos: 3822059520 flags: 0600001 ... pos: 3968860160 flags: 0600001 ... pos: 4107272192 flags: 0600001 Actual result: In the flags in step 6 output, the third value is '0' which stands for 'auto_dump_bypass_cache' is disabled. The system did not bypass the cache for auto dump with auto_dump_bypass_cache enabled. Expect result: In the flags in step 6 output, the third value is '4' which stands for 'auto_dump_bypass_cache' is enabled. The system should bypass the cache for auto dump with auto_dump_bypass_cache enabled.