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

Jia-Ju Bai : > > On 2018/1/19 9:11, Francois Romieu wrote: > > Jia-Ju Bai : > > [...] > > > The function rtl8169_start_xmit reads tp->dirty_tx in TX_FRAGS_READY_FOR: > > > if (unlikely(!TX_FRAGS_READY_FOR(tp, skb_shinfo(skb)->nr_frags))) { >

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

Peter Zijlstra : > On Fri, Jan 19, 2018 at 02:11:18AM +0100, Francois Romieu wrote: > > Peter Zijlstra : > > [...] > > > There is only 1 variable afaict. Memory barriers need at least 2 in > > > order to be able to do _anything_. > > > > I don't get

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

On Fri, Jan 19, 2018 at 02:11:18AM +0100, Francois Romieu wrote: > Peter Zijlstra : > [...] > > 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

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

On 2018/1/19 9:11, Francois Romieu wrote: Jia-Ju Bai : [...] The function rtl8169_start_xmit reads tp->dirty_tx in TX_FRAGS_READY_FOR: if (unlikely(!TX_FRAGS_READY_FOR(tp, skb_shinfo(skb)->nr_frags))) { netif_err(tp, drv, dev, "BUG! Tx Ring full when

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

Jia-Ju Bai : [...] > The function rtl8169_start_xmit reads tp->dirty_tx in TX_FRAGS_READY_FOR: > if (unlikely(!TX_FRAGS_READY_FOR(tp, skb_shinfo(skb)->nr_frags))) { > netif_err(tp, drv, dev, "BUG! Tx Ring full when queue awake!\n"); > goto err_stop_0; >

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

Peter Zijlstra : [...] > 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 ? -- Ueimor

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

On Thu, Jan 18, 2018 at 10:06:17PM +0800, Jia-Ju Bai wrote: > In the rt8169 driver, the function "rtl_tx" uses "smp_mb" to sync the > writing operation with rtl8169_start_xmit: > if (tp->dirty_tx != dirty_tx) { > tp->dirty_tx = dirty_tx; > smp_mb(); > ... > } > The

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

In the rt8169 driver, the function "rtl_tx" uses "smp_mb" to sync the writing operation with rtl8169_start_xmit: if (tp->dirty_tx != dirty_tx) { tp->dirty_tx = dirty_tx; smp_mb(); ... } The function rtl8169_start_xmit reads tp->dirty_tx in TX_FRAGS_READY_FOR: