Driver patch to look at...

[John Baldwin]

On Tuesday, February 05, 2013 2:08:15 pm Randall Stewart wrote:
> Hmm
> 
> wait, I could probably do the compare to whats in the ring buffer ;-D

I wouldn't bother.  The compare and branch is probably more expensive than
the store.

> R
> On Feb 5, 2013, at 2:04 PM, Randall Stewart wrote:
> 
> > Hmm
> > 
> > That would trade off a stack pointer + a compare
> > vs always doing the move.
> > 
> > Thats fine until I have to add the _mc() version, then the put
> > back would be an atomic, and most of the time the return from
> > this is probably not changed…
> > 
> > I really would prefer not to since the compare and maybe store vs
> > the always store.. though the same now, would be far more expensive
> > in the _mc version.. if we do a _mc version of course ;-)
> > 
> > But I am willing to do whatever .. since this really needs to be fixed.
> > 
> > R
> > On Feb 5, 2013, at 1:52 PM, John Baldwin wrote:
> > 
> >> On Tuesday, February 05, 2013 12:44:01 pm Randall Stewart wrote:
> >>> Actually, no it is used.
> >>> 
> >>> If you look in if_var.h int he drbr_putback() function, it does
> >>> a buf_ring_swap when the old mbuf pointer does not equal the
> >>> new mbuf pointer. This *does* happen, I crashed at least once
> >>> yesterday when the igb driver did something to free the original
> >>> mbuf and return a new mbuf with the data (prepend or some such).
> >>> 
> >>> I also have found several issues that I have fixed this morning.. its been
> >>> crash city on my test beds..
> >>> 
> >>> Here is the latest patch with all fixes and suggested changes from emaste 
> >> (thanks Ed)
> >> 
> >> Actually, one more suggestion then (since you have to keep putback).  It
> >> would be nice to not have to require 'snext' in all the callers.  How
> >> about replace buf_ring_swap() with a buf_ring_putback_sc() that accepts the
> >> mbuf and just stores it at the head unconditionally and have drbr_putback()
> >> use that?
> >> 
> >> -- 
> >> John Baldwin
> >> _______________________________________________
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> >> 
> > 
> > ------------------------------
> > Randall Stewart
> > 803-317-4952 (cell)
> > 
> > _______________________________________________
> > freebsd-net at freebsd.org mailing list
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> > 
> 
> ------------------------------
> Randall Stewart
> 803-317-4952 (cell)
> 
> 

-- 
John Baldwin