Re: increase size of number of possible tracing events

On Fri, 21 Jun 2019 18:14:54 -0400
Anthony Eden <[email protected]> wrote:

> I am trying to develop a patch which increases the maximum number of
> possible tracing events (i.e. TRACE_EVENT_TYPE_MAX). I naively tried
> changing unsigned short trace_entry::type to unsigned int (that simply
> broke tracing).
> 
> Short background: I am placing a UProbe tracepoint at the start of
> every basic block for every DSO in a dynamically-linked program. I
> recently hit the ceiling for the maximum number of tracepoints with
> dnsmasq;
> 
> /usr/bin/dnsmasq:            12826 basic blocks
> /usr/lib/libc.so.6:          60511 basic blocks
> /lib64/ld-linux-x86-64.so.2: 6270 basic blocks
> linux-vdso.so.1:             36 basic blocks
> 
> Writing to /sys/kernel/debug/tracing/uprobe_events returns -ENODEV. If
> anyone could provide some guidance towards raising the limit, it would
> be much appreciated.
>

I'm not sure having over 65535 different events is a good idea. Perhaps
we should create a different type of uprobe that can be reused, as I'm
sure you are not making each of these events record different data.
Basically make it similar to the function tracing event, which is a
single event that records the function that it traces, and not
thousands of different individual events.

Would something like that be helpful for you? It still requires a
kernel change, but that is still possible.

-- Steve