On Fri, 2020-09-04 at 12:35 +0200, Greg KH wrote: > On Fri, Sep 04, 2020 at 11:53:42AM +0206, John Ogness wrote: > > On 2020-09-04, Changki Kim <[email protected]> wrote: > > > Printk() meesages are the most basic and useful debug method. > > > However, additional information needs in multi-processor. > > > If we add messages with processor id and process name, we can find > > > a problem only with messages when the problem occurs with H/W IP or CPU. > > > This is very useful in narrowing down the scope of the problems. > > > > [...] > > > > > diff --git a/kernel/printk/printk_ringbuffer.h > > > b/kernel/printk/printk_ringbuffer.h > > > index e6302da041f9..fcefe9516606 100644 > > > --- a/kernel/printk/printk_ringbuffer.h > > > +++ b/kernel/printk/printk_ringbuffer.h > > > @@ -21,6 +22,12 @@ struct printk_info { > > > u8 flags:5; /* internal record flags */ > > > u8 level:3; /* syslog level */ > > > u32 caller_id; /* thread id or processor id */ > > > +#ifdef CONFIG_PRINTK_PROCESS > > > + int pid; /* process id */ > > > + u8 cpu_id; /* processor id */ > > > + u8 in_interrupt; /* interrupt conext */ > > > + char process[TASK_COMM_LEN]; /* process name */ > > > +#endif > > > }; > > > > I can understand the desire to have more information with messages. But > > IMHO adding it to the ringbuffer descriptor is the wrong place for > > it. The descriptor should really be limited to data that the printk > > subsystem needs for _itself_. With respect to LOG_CONT, I think we can > > agree that @caller_id is not enough. But there has been discussions [0] > > of having @caller_id provide a better context representation. > > > > If we want to support adding more meta information to messages, I would > > prefer that the information is either prepended directly to the message > > text string or appended to the dictionary text string. We could even go > > so far as providing a boot argument where a list of information could be > > specified, what should be automatically added to the text/dict strings > > of each message. That would not require any ringbuffer changes and would > > allow new types of information to be added later. > > > > Something like: > > > > printk.format=ts,cpu,comm,pid,in_atomic > > > > John Ogness > > > > [0] https://lkml.kernel.org/r/[email protected] > > Ah, finally a good use of the "dictionary" that we all can agree makes > sense :) > > This does seem like a better solution overall, thanks.
__func__ too please so that it could optionally be enabled per subsystem using %pS, __builtin_return_address(<appropriate_level>) That way a lot of %s:..., __func__ could be removed from specific printk instances.
