* [PATCH net-next 1/4] r8169: use smp_store_mb in rtl_tx
2020-04-19 17:38 [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
@ 2020-04-19 17:39 ` Heiner Kallweit
2020-04-19 17:41 ` [PATCH net-next 2/4] r8169: change wmb to dma_wmb in rtl8169_start_xmit Heiner Kallweit
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Heiner Kallweit @ 2020-04-19 17:39 UTC (permalink / raw)
To: Realtek linux nic maintainers, David Miller; +Cc: netdev
Use helper smp_store_mb() instead of open-coding the functionality.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
drivers/net/ethernet/realtek/r8169_main.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 1bc415d00..dd6113fd7 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -4438,7 +4438,6 @@ static void rtl_tx(struct net_device *dev, struct rtl8169_private *tp,
tp->tx_stats.bytes += bytes_compl;
u64_stats_update_end(&tp->tx_stats.syncp);
- tp->dirty_tx = dirty_tx;
/* Sync with rtl8169_start_xmit:
* - publish dirty_tx ring index (write barrier)
* - refresh cur_tx ring index and queue status (read barrier)
@@ -4446,7 +4445,7 @@ static void rtl_tx(struct net_device *dev, struct rtl8169_private *tp,
* a racing xmit thread can only have a right view of the
* ring status.
*/
- smp_mb();
+ smp_store_mb(tp->dirty_tx, dirty_tx);
if (netif_queue_stopped(dev) &&
rtl_tx_slots_avail(tp, MAX_SKB_FRAGS)) {
netif_wake_queue(dev);
--
2.26.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next 2/4] r8169: change wmb to dma_wmb in rtl8169_start_xmit
2020-04-19 17:38 [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
2020-04-19 17:39 ` [PATCH net-next 1/4] r8169: use smp_store_mb in rtl_tx Heiner Kallweit
@ 2020-04-19 17:41 ` Heiner Kallweit
2020-04-19 17:42 ` [PATCH net-next 3/4] r8169: replace dma_rmb with READ_ONCE in rtl_rx Heiner Kallweit
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Heiner Kallweit @ 2020-04-19 17:41 UTC (permalink / raw)
To: Realtek linux nic maintainers, David Miller; +Cc: netdev
It's the typical dma_wmb() use case to finish descriptor writes before
ringing the device doorbell. Therefore switch to this lighter barrier.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
drivers/net/ethernet/realtek/r8169_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index dd6113fd7..038cd6fde 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -4259,7 +4259,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
txd_first->opts1 |= cpu_to_le32(DescOwn | FirstFrag);
/* Force all memory writes to complete before notifying device */
- wmb();
+ dma_wmb();
tp->cur_tx += frags + 1;
--
2.26.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next 3/4] r8169: replace dma_rmb with READ_ONCE in rtl_rx
2020-04-19 17:38 [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
2020-04-19 17:39 ` [PATCH net-next 1/4] r8169: use smp_store_mb in rtl_tx Heiner Kallweit
2020-04-19 17:41 ` [PATCH net-next 2/4] r8169: change wmb to dma_wmb in rtl8169_start_xmit Heiner Kallweit
@ 2020-04-19 17:42 ` Heiner Kallweit
2020-04-19 17:44 ` [PATCH net-next 4/4] r8169: use WRITE_ONCE instead of dma_wmb in rtl8169_mark_to_asic Heiner Kallweit
2020-04-19 18:11 ` [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
4 siblings, 0 replies; 6+ messages in thread
From: Heiner Kallweit @ 2020-04-19 17:42 UTC (permalink / raw)
To: Realtek linux nic maintainers, David Miller; +Cc: netdev
We want to ensure that desc->opts1 is read before desc->opts2.
This doesn't require a full compiler barrier. READ_ONCE provides
the ordering guarantee we need.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
drivers/net/ethernet/realtek/r8169_main.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)
diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 038cd6fde..df788063e 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -1548,7 +1548,7 @@ static inline u32 rtl8169_tx_vlan_tag(struct sk_buff *skb)
static void rtl8169_rx_vlan_tag(struct RxDesc *desc, struct sk_buff *skb)
{
- u32 opts2 = le32_to_cpu(desc->opts2);
+ u32 opts2 = le32_to_cpu(READ_ONCE(desc->opts2));
if (opts2 & RxVlanTag)
__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), swab16(opts2 & 0xffff));
@@ -4490,16 +4490,11 @@ static int rtl_rx(struct net_device *dev, struct rtl8169_private *tp, u32 budget
struct RxDesc *desc = tp->RxDescArray + entry;
u32 status;
- status = le32_to_cpu(desc->opts1);
+ /* Use READ_ONCE to order descriptor field reads */
+ status = le32_to_cpu(READ_ONCE(desc->opts1));
if (status & DescOwn)
break;
- /* This barrier is needed to keep us from reading
- * any other fields out of the Rx descriptor until
- * we know the status of DescOwn
- */
- dma_rmb();
-
if (unlikely(status & RxRES)) {
netif_info(tp, rx_err, dev, "Rx ERROR. status = %08x\n",
status);
--
2.26.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH net-next 4/4] r8169: use WRITE_ONCE instead of dma_wmb in rtl8169_mark_to_asic
2020-04-19 17:38 [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
` (2 preceding siblings ...)
2020-04-19 17:42 ` [PATCH net-next 3/4] r8169: replace dma_rmb with READ_ONCE in rtl_rx Heiner Kallweit
@ 2020-04-19 17:44 ` Heiner Kallweit
2020-04-19 18:11 ` [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
4 siblings, 0 replies; 6+ messages in thread
From: Heiner Kallweit @ 2020-04-19 17:44 UTC (permalink / raw)
To: Realtek linux nic maintainers, David Miller; +Cc: netdev
We want to ensure that desc->opts1 is written as last descriptor field.
This doesn't require a full compiler barrier, WRITE_ONCE provides the
ordering guarantee we need.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
drivers/net/ethernet/realtek/r8169_main.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index df788063e..8e9944692 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -3892,11 +3892,9 @@ static inline void rtl8169_mark_to_asic(struct RxDesc *desc)
{
u32 eor = le32_to_cpu(desc->opts1) & RingEnd;
- desc->opts2 = 0;
- /* Force memory writes to complete before releasing descriptor */
- dma_wmb();
-
- desc->opts1 = cpu_to_le32(DescOwn | eor | R8169_RX_BUF_SIZE);
+ /* Ensure ordering of writes */
+ WRITE_ONCE(desc->opts2, 0);
+ WRITE_ONCE(desc->opts1, cpu_to_le32(DescOwn | eor | R8169_RX_BUF_SIZE));
}
static struct page *rtl8169_alloc_rx_data(struct rtl8169_private *tp,
@@ -3919,7 +3917,7 @@ static struct page *rtl8169_alloc_rx_data(struct rtl8169_private *tp,
return NULL;
}
- desc->addr = cpu_to_le64(mapping);
+ WRITE_ONCE(desc->addr, cpu_to_le64(mapping));
rtl8169_mark_to_asic(desc);
return data;
--
2.26.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH net-next 0/4] r8169: improve memory barriers
2020-04-19 17:38 [PATCH net-next 0/4] r8169: improve memory barriers Heiner Kallweit
` (3 preceding siblings ...)
2020-04-19 17:44 ` [PATCH net-next 4/4] r8169: use WRITE_ONCE instead of dma_wmb in rtl8169_mark_to_asic Heiner Kallweit
@ 2020-04-19 18:11 ` Heiner Kallweit
4 siblings, 0 replies; 6+ messages in thread
From: Heiner Kallweit @ 2020-04-19 18:11 UTC (permalink / raw)
To: Realtek linux nic maintainers, David Miller; +Cc: netdev
On 19.04.2020 19:38, Heiner Kallweit wrote:
> This series includes improvements for (too heavy) memory barriers.
> Tested on x86-64 with RTL8168g chip version.
>
> Heiner Kallweit (4):
> r8169: use smp_store_mb in rtl_tx
> r8169: change wmb to dma_wmb in rtl8169_start_xmit
I think I'll have to drip this patch from the series. These Realtek
chips are also used on non-x86 platforms, and these platforms may
not be coherent. I'll send a v2.
> r8169: replace dma_rmb with READ_ONCE in rtl_rx
> r8169: use WRITE_ONCE instead of dma_wmb in rtl8169_mark_to_asic
>
> drivers/net/ethernet/realtek/r8169_main.c | 26 ++++++++---------------
> 1 file changed, 9 insertions(+), 17 deletions(-)
>
^ permalink raw reply [flat|nested] 6+ messages in thread