Re: net: r8169: a question of memory barrier in the r8169 driver

Peter Zijlstra [off-list ref] :

On Fri, Jan 19, 2018 at 02:11:18AM +0100, Francois Romieu wrote:

quoted

Peter Zijlstra [off-list ref] :
[...]

quoted

There is only 1 variable afaict. Memory barriers need at least 2 in
order to be able to do _anything_.

I don't get your point: why don't {cur_tx, dirty_tx} qualify as said
two variables ?

There wasn't any cur_tx in the code you provided.

/* A skbuff with nr_frags needs nr_frags+1 entries in the tx queue */
#define TX_FRAGS_READY_FOR(tp,nr_frags) \
        (TX_SLOTS_AVAIL(tp) >= (nr_frags + 1))

#define TX_SLOTS_AVAIL(tp) \
        (tp->dirty_tx + NUM_TX_DESC - tp->cur_tx)

Both are also used in rtl_tx.

I don't get your point. Even a single variable is scattered through
the system.

-- 
Ueimor