RE: [patch] printk subsystems

[Tom Zanussi <zanussi@us.ibm.com>]

Perez-Gonzalez, Inaky writes:
 > 
 > > From: Tom Zanussi [mailto:zanussi@us.ibm.com]
 > > 
 > > It seems to me that when comparing apples to apples, namely
 > > considering the complete lifecycle of an event, ... <snip>
 > > 
 > > While kue_send_event() in itself is very simple and efficient, it's
 > > only part of the story, the other parts being the copy_to_user() ...
 > 
 > Agreed - my mistake here in the comparison for leaving out that stuff.
 > 
 > > event.  While kue can avoid this kernel-side copy, it's not possible
 > > for it to avoid the copy_to_user() since its design precludes mmapping
 > > the kernel data.  Again, six of one, half dozen of another.  kue looks
 > 
 > Sure - those things, I would say, they compensate one another, 
 > except for that mmap() detail that pushes the balance towards relayfs
 > regarding effectiveness when delivering the messages; I think that
 > at the end the difference should not be too big as the copying of
 > the data in kue to user space should roughly compensate by the copying
 > of the data to the relayfs buffer; after all, a copy is a copy.
 > No data to back this claim though, I am just thinking a mental 
 > schematic of the lifetime of a bit in both systems out loud.
 > 

Right.  This is what I meant when I said the two were very similar
when considering the lifetime of a single event, ignoring everything
else such as bulk processing via mmap() vs. iterating through a list,
as discussed elsewhere.

 > Or, again, I am missing something ...
 > 
 > Iñaky Pérez-González -- Not speaking for Intel -- all opinions are my own
 > (and my fault)
 > 

-- 
Regards,

Tom Zanussi <zanussi@us.ibm.com>
IBM Linux Technology Center/RAS