[Xen-devel] How to read the xen format file and the generated trace content ?

[Mahendra Kutare <mahendra.kutare@xxxxxxxxx>]

Hi All,

I am trying to understand the format file which comes with too/xentrace/formats.

If anyone can help in understanding the following, that will be great -

Take for example -

0x0002800e  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  switch_infprev    [
old_domid = 0x%(1)08x, runtime = %(2)d ]
0x0002800f  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  switch_infnext    [
new_domid = 0x%(1)08x, time = %(2)d, r_time = %(3)d ]

In the above format rule,

1. Can anyone point me to the source code that populates the cpu and
tsc using xentrace data ?

2. In the above, I understand 1, 2 and 3 means first, second and third
field from the TRACE but what does the whole field description means
i.e.

0x%(1)08x apart from the fact that it represents hexadecimal value for DOM IDs.

If above represents DOM ID values then from the trace data generated like this -

CPU0  7997860846654673 (+    4133)  switch_infprev    [ old_domid =
0x00007fff, runtime = 79935 ]
CPU0  7997860846655190 (+     517)  switch_infnext    [ new_domid =
0x00000000, time = 3889, r_time = 30000000 ]

old_domid = 0x00007fff represents 32767 for some some DOM ID.  There
is no domain which has been assigned the 32767 id  or for that matter
DOM0.

new_domid =  0x00000000 represents 0 which is clearly the DOM0 id.

So what is this old_domid value means ? Or is it just some junk value
? My understanding was the SWITCH_INFPREV traces the domain to be
descheduled and SWITCH_INFNEXT traces to be scheduled. If thats the
case, then why is current DOM ID a junk value.

Any pointer to the the source code to understand this better will be helpful.

If I look at xm list it shows -
[root@samoa3 mahendra 04:13 PM]$ xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0  1022     8     r-----  94726.9
mapache                                     24   256     1     -b----    739.7
mmysql                                      22   256     1     -b----     99.1
mtomcat                                     23   256     1     -b----    522.4

So for Domain-0 with DOM ID of 0 makes sense but what about the OLD
DOM ID value.

If I look at another trace record -

CPU0  7997860846373115 (+    2130)  domain_wake       [ domid =
0x00000018, edomid = 0x00000000 ]

Here, it make sense that domid is 24 which is mpache domain as listed
by xm list.

Can anyone help me understand this and point to relevant source code ?

Thanks
Mahendra

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