Re: [PATCH] KVM: Create debugfs statistics for each VM

[Janosch Frank <frankja@linux.vnet.ibm.com>]

On 02/01/2016 12:45 PM, Christian Borntraeger wrote:
> On 01/28/2016 04:49 PM, Janosch Frank wrote:
>> KVM statistics for VMs (no. of exits, halts and other special
>> instructions) are currently only available in a summarized manner for
>> all VMs. They are exported to userland through files in the kvm
>> debugfs directory and used for performance monitoring, as well as VM
>> problem detection with helper tools like kvm_stat. If a VM has
>> problems and therefore creates a large number of exits, one can not
>> easily find out which one it is, as there is no VM specific data.
>>
>> This patch adds a kvm debugfs subdirectory for each VM, which is named
>> after its pid and file descriptor. They contain the same kind of files
>> that are already in the kvm debugfs directory, but the data that is
>> exported through them is now VM specific.
>>
>> CC: Dan Carpenter <dan.carpenter@oracle.com> [includes fixes by Dan Carpenter]
>> Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
> 
> for s390:
> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> 
> 
> 
> some questions below
> 
> [...]
>>
>> +/* Worst case buffer size needed for holding an integer. */
>> +#define ITOA_MAX_LEN 12
> 
> 4294967295 has 10, so this is to cover the \0 and a potential "-", correct?

Correct
For the dir name we have 2 * ITOA_MAX_LEN, as it is %d-%d an we only
need one \0 which accounts for the additional hyphen.
I'm open for suggestions about how to make this clearer.

> 
> 
> [...]
>> @@ -3436,7 +3602,8 @@ static int kvm_init_debug(void)
>>  	if (kvm_debugfs_dir == NULL)
>>  		goto out;
>>
>> -	for (p = debugfs_entries; p->name; ++p) {
>> +	kvm_debugfs_num_entries = 0;
>> +	for (p = debugfs_entries; p->name; ++p, kvm_debugfs_num_entries++) {
> 
> Looks like we cannot use ARRAY_SIZE(kvm_stats_debugfs_item), so unless somebody
> has a better idea we have to stick with kvm_debugfs_num_entries being calculated.
> 
> 
>>  		if (!debugfs_create_file(p->name, 0444, kvm_debugfs_dir,
>>  					 (void *)(long)p->offset,
>>  					 stat_fops[p->kind]))
>>
>