Re: [PATCH v2 21/27] coresight: Convert driver messages to dev_dbg

From: Robert Walker
Date: Wed May 02 2018 - 04:26:29 EST


On 02/05/18 04:55, Kim Phillips wrote:
On Tue, 1 May 2018 10:10:51 +0100
Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:

Convert component enable/disable messages from dev_info to dev_dbg.
This is required to prevent LOCKDEP splats when operating in perf
mode where we could be called with locks held to enable a coresight
Can we see the splats? Doesn't lockdep turn itself off if it starts
triggering too many splats?

path. If someone wants to really see the messages, they can always
enable it at runtime via dynamic_debug.
Won't the splats still occur when the messages are enabled with
dynamic_debug?

So in effect this patch only tries to mitigate the splats, all the
while making things harder for regular users that now have to recompile
their kernels, in exchange for a very small convenience for kernel
developers that happen to see a splat or two with DEBUG_LOCKDEP set?

Not the greatest choice...How about moving the dev_infos outside of the
locks instead?

Thanks,

Kim
The other reason for making these dev_dbg is performance - a message is output each time a source / link / sink is enabled or disabled, so we can get 20+ messages on each process switch when tracing with perf. This has a significant effect on the runtime of the application being traced.

Regards

Rob