Re: [PATCH v2 2/2] sunrpc: add a Kconfig option to redirect dfprintk() output to trace buffer

[Chuck Lever <chuck.lever@oracle.com>]

On 8/22/25 9:19 AM, Jeff Layton wrote:
> We have a lot of old dprintk() call sites that aren't going anywhere
> anytime soon. At the same time, turning them up is a serious burden on
> the host due to the console locking overhead.
> 
> Add a new Kconfig option that redirects dfprintk() output to the trace
> buffer. This is more efficient than logging to the console and allows
> for proper interleaving of dprintk and static tracepoint events.
> 
> Since using trace_printk() causes scary warnings to pop at boot time,
> this new option defaults to "n".
> 
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  include/linux/sunrpc/debug.h | 10 ++++++++--
>  net/sunrpc/Kconfig           | 14 ++++++++++++++
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/sunrpc/debug.h b/include/linux/sunrpc/debug.h
> index 99a6fa4a1d6af0b275546a53957f07c9a509f2ac..891f6173c951a6644018237017c845d81b42aa76 100644
> --- a/include/linux/sunrpc/debug.h
> +++ b/include/linux/sunrpc/debug.h
> @@ -30,17 +30,23 @@ extern unsigned int		nlm_debug;
>  #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
>  # define ifdebug(fac)		if (unlikely(rpc_debug & RPCDBG_##fac))
>  
> +# if IS_ENABLED(CONFIG_SUNRPC_DEBUG_TRACE)
> +#  define __sunrpc_printk(fmt, ...)	trace_printk(fmt, ##__VA_ARGS__)
> +# else
> +#  define __sunrpc_printk(fmt, ...)	printk(KERN_DEFAULT fmt, ##__VA_ARGS__)
> +# endif
> +
>  # define dfprintk(fac, fmt, ...)					\
>  do {									\
>  	ifdebug(fac)							\
> -		printk(KERN_DEFAULT fmt, ##__VA_ARGS__);				\
> +		__sunrpc_printk(fmt, ##__VA_ARGS__);			\
>  } while (0)
>  
>  # define dfprintk_rcu(fac, fmt, ...)					\
>  do {									\
>  	ifdebug(fac) {							\
>  		rcu_read_lock();					\
> -		printk(KERN_DEFAULT fmt, ##__VA_ARGS__);				\
> +		__sunrpc_printk(fmt, ##__VA_ARGS__);			\
>  		rcu_read_unlock();					\
>  	}								\
>  } while (0)
> diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig
> index 2d8b67dac7b5b58a8a86c3022dd573746fb22547..a570e7adf270fb8976f751266bbffe39ef696c6a 100644
> --- a/net/sunrpc/Kconfig
> +++ b/net/sunrpc/Kconfig
> @@ -101,6 +101,20 @@ config SUNRPC_DEBUG
>  
>  	  If unsure, say Y.
>  
> +config SUNRPC_DEBUG_TRACE
> +	bool "RPC: Send dfprintk() output to the trace buffer"
> +	depends on SUNRPC_DEBUG && TRACING
> +	default n
> +	help
> +          dprintk() output can be voluminous, which can overwhelm the
> +          kernel's logging facility as it must be sent to the console.
> +          This option causes dprintk() output to go to the trace buffer
> +          instead of the kernel log.
> +
> +          This will cause warnings about trace_printk() being used to be
> +          logged at boot time, so say N unless you are debugging a problem
> +          with sunrpc-based clients or services.
> +
>  config SUNRPC_XPRT_RDMA
>  	tristate "RPC-over-RDMA transport"
>  	depends on SUNRPC && INFINIBAND && INFINIBAND_ADDR_TRANS
> 

Nice and surgical. But I'm on the fence about whether this is a
good long-term strategy. No real objections, though.

Reviewed-by: Chuck Lever <chuck.lever@oracle.com>


-- 
Chuck Lever