[libvirt] [v7 00/10] Support cache tune in libvirt

[Martin Kletzander]

On Mon, Feb 20, 2017 at 04:32:19PM +0800, Eli Qiao wrote:
>
>
>--
>Best regards
>Eli
>
>天涯无处不重逢
>a leaf duckweed belongs to the sea, where not to meet in life
>
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>
>
>On Sunday, 19 February 2017 at 10:51 PM, Marcelo Tosatti wrote:
>
>>
>> Hi Eli Qiao,
>>
>> Question about removing resctrlfs directories with empty "tasks" file.
>>
>>
>> /* This domain is not created by libvirt, so we don't care
>> * about the tasks, add a fake one to prevent
>> * virResCtrlRefresh
>> * remove it from sysfs */
>> virResCtrlAddTask(p, 1);
>> virResCtrlAppendDomain(p);
>>
>> /* Refresh all domains', remove the domains which has no task ids.
>> * This will be used after VM pause, restart, destroy etc.
>> */
>> static int
>> virResCtrlRefresh(void)
>>
>> Why are you doing this (removing directories which have no tasks in
>> them) ? The code should only read information from other
>> CAT reservations, not write to them.
>>
>>
>When a VM get shutdown, their pids will disappear from resctrl’s directory, we can check pids to see if VM get KIlled or not.
>
>The reason why I would like check if tasks file empty is that: there maybe cases that libvirtd not tracking VM’s status, and the VM gone, left a empty directory with no tasks assigned, and cause resource leak.
>
>I think I can refine this later, keep a pointer of ResDomain in VM’s private data and use that to destroy VM’s resctrl directory.
>
>but this won’t work for exception, still resource leak happened.
>

Function qemuProcessStop() will *always* be called to cleanup after VMs,
all exceptions should be taken into account, so don't worry, just do
proper cleanup.

>> This is not for cleanup purposes, since on VM shutdown the resctrlfs
>> directories are properly removed:
>>
>> /* Remove the Domain from sysfs, this should only success no pids in
>> * tasks
>> * of a partition.
>> */
>> static
>> int virResCtrlRemoveDomain(const char *name)
>> {
>> char *path = NULL;
>> int rc = 0;
>>
>> if ((rc = virAsprintf(&path, "%s/%s", RESCTRL_DIR, name)) < 0)
>> return rc;
>> rc = rmdir(path);
>> VIR_FREE(path);
>> return rc;
>> }
>>
>> Should not write to other directories 'tasks' file.
>
>Other Apps can have a lock to resctrl before it write tasks to prevent libvirtd remove empty task directory.
>
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