'-c' flag and kernel pages isolation

[RainM]

Hi, Andi

You wrote that '-c' flag doesn't work because of kernel page isolation.
Could you help me to understand how simple-pt deals with processes. How does simple-pt distinguish one process from another? According to what I see at simple-pt.c you set some trace points to scheduler in order to handle context switch and save this information somewhere? Is it right?
And you mentioned that now a process have multiple page tables. Am I right that the purpose of this is to handle different address spaces for application and kernel?
Since it works this way nowadays, how to extract a trace for a specified TID/PID from simple-pt trace? I talk about hypothetical availability for such thing even is this requires writing code.

--Sergey

[andikleen]

On Wed, May 15, 2019 at 07:09:49AM -0700, Sergey Melnikov wrote: Hi, Andi You wrote that '-c' flag doesn't work because of kernel page isolation.

It actually works, but only for kernel code. User code has different page tables, so it won't match the filter.

Could you help me to understand how simple-pt deals with proces

It uses the address of the page tables to identify or filter the process. The filtering is done using a hardware filter in the CPU that can match on the page table address.

…

-Andi