| Message ID | 20180525041321.140516-1-venkateshs@google.com |
|---|---|
| State | Accepted |
| Delegated to: | Jeff Kirsher |
| Headers | show |
| Series | igb: Use dma_wmb() instead of wmb() before doorbell writes | expand |
On Thu, May 24, 2018 at 9:13 PM, Venkatesh Srinivas <venkateshs@google.com> wrote: > igb writes to doorbells to post transmit and receive descriptors; > after writing descriptors to memory but before writing to doorbells, > use dma_wmb() rather than wmb(). wmb() is more heavyweight than > necessary before doorbell writes. > > On x86, this avoids SFENCEs before doorbell writes in both the > tx and rx refill paths. > > Signed-off-by: Venkatesh Srinivas <venkateshs@google.com> > --- > drivers/net/ethernet/intel/igb/igb_main.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c > index cce7ada89255..8aea50867a5d 100644 > --- a/drivers/net/ethernet/intel/igb/igb_main.c > +++ b/drivers/net/ethernet/intel/igb/igb_main.c > @@ -5674,7 +5674,7 @@ static int igb_tx_map(struct igb_ring *tx_ring, > * We also need this memory barrier to make certain all of the > * status bits have been updated before next_to_watch is written. > */ > - wmb(); > + dma_wmb(); > > /* set next_to_watch value indicating a packet is present */ > first->next_to_watch = tx_desc; This change I am good with. My first instinct would be to replace this with just an smp_wmb(), however we are better off probably just using the dma_wmb() so that it doesn't get compiled out in the non-smp kernel case. > @@ -8093,7 +8093,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 cleaned_count) > * applicable for weak-ordered memory model archs, > * such as IA-64). > */ > - wmb(); > + dma_wmb(); > writel(i, rx_ring->tail); > } > } I'm not sure if this is even really needed. My understanding is that the writel should be providing a barrier if needed already. Odds are we can probably just drop the wmb() and update the comment that goes with it. Thanks. - Alex
> From: Intel-wired-lan [mailto:intel-wired-lan-bounces@osuosl.org] On > Behalf Of Alexander Duyck > Sent: Friday, May 25, 2018 8:56 AM > To: Venkatesh Srinivas <venkateshs@google.com> > Cc: vsrinivas@ops101.org; intel-wired-lan <intel-wired-lan@lists.osuosl.org> > Subject: Re: [Intel-wired-lan] [PATCH] igb: Use dma_wmb() instead of wmb() > before doorbell writes > > On Thu, May 24, 2018 at 9:13 PM, Venkatesh Srinivas > <venkateshs@google.com> wrote: > > igb writes to doorbells to post transmit and receive descriptors; > > after writing descriptors to memory but before writing to doorbells, > > use dma_wmb() rather than wmb(). wmb() is more heavyweight than > > necessary before doorbell writes. > > > > On x86, this avoids SFENCEs before doorbell writes in both the > > tx and rx refill paths. > > > > Signed-off-by: Venkatesh Srinivas <venkateshs@google.com> > > --- > > drivers/net/ethernet/intel/igb/igb_main.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) Tested-by: Aaron Brown <aaron.f.brown@intel.com>
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c index cce7ada89255..8aea50867a5d 100644 --- a/drivers/net/ethernet/intel/igb/igb_main.c +++ b/drivers/net/ethernet/intel/igb/igb_main.c @@ -5674,7 +5674,7 @@ static int igb_tx_map(struct igb_ring *tx_ring, * We also need this memory barrier to make certain all of the * status bits have been updated before next_to_watch is written. */ - wmb(); + dma_wmb(); /* set next_to_watch value indicating a packet is present */ first->next_to_watch = tx_desc; @@ -8093,7 +8093,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 cleaned_count) * applicable for weak-ordered memory model archs, * such as IA-64). */ - wmb(); + dma_wmb(); writel(i, rx_ring->tail); } }
igb writes to doorbells to post transmit and receive descriptors; after writing descriptors to memory but before writing to doorbells, use dma_wmb() rather than wmb(). wmb() is more heavyweight than necessary before doorbell writes. On x86, this avoids SFENCEs before doorbell writes in both the tx and rx refill paths. Signed-off-by: Venkatesh Srinivas <venkateshs@google.com> --- drivers/net/ethernet/intel/igb/igb_main.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)