| Message ID | 1368482311.3305.48.camel@bwh-desktop.uk.solarflarecom.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
> The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no > need for this optimisation any more. Hmmm.... even on x86 there will be a measurable cost in misaligned accesses - at least for some workloads. If the DMA is able to write to a mis-aligned buffer and still perform aligned burst transfers mid-frame then 4n+2 aligning the rx buffer should be a win even on x86. Note to hardware engineers: add an option to write two bytes of junk before the rx data :-) David
On Tue, 2013-05-14 at 09:32 +0100, David Laight wrote: > > The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > > (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no > > need for this optimisation any more. > > Hmmm.... even on x86 there will be a measurable cost > in misaligned accesses - at least for some workloads. When they cross cache-line boundaries, yes. Maybe napi_get_frags() should be adding the 2 byte offset on all architectures, as the skbs it allocates are never RX DMA buffers. > If the DMA is able to write to a mis-aligned buffer and > still perform aligned burst transfers mid-frame then > 4n+2 aligning the rx buffer should be a win even on x86. I don't think so. > Note to hardware engineers: add an option to write two > bytes of junk before the rx data :-) There is some hardware with that option. Ben.
From: Ben Hutchings <bhutchings@solarflare.com> Date: Mon, 13 May 2013 22:58:31 +0100 > The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no > need for this optimisation any more. > > Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c index 01b9920..999289b 100644 --- a/drivers/net/ethernet/sfc/efx.c +++ b/drivers/net/ethernet/sfc/efx.c @@ -638,13 +638,13 @@ static void efx_start_datapath(struct efx_nic *efx) EFX_MAX_FRAME_LEN(efx->net_dev->mtu) + efx->type->rx_buffer_padding); rx_buf_len = (sizeof(struct efx_rx_page_state) + - EFX_PAGE_IP_ALIGN + efx->rx_dma_len); + NET_IP_ALIGN + efx->rx_dma_len); if (rx_buf_len <= PAGE_SIZE) { efx->rx_scatter = false; efx->rx_buffer_order = 0; } else if (efx->type->can_rx_scatter) { BUILD_BUG_ON(sizeof(struct efx_rx_page_state) + - EFX_PAGE_IP_ALIGN + EFX_RX_USR_BUF_SIZE > + NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE > PAGE_SIZE / 2); efx->rx_scatter = true; efx->rx_dma_len = EFX_RX_USR_BUF_SIZE; diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h index 9bd433a..5efddf3 100644 --- a/drivers/net/ethernet/sfc/net_driver.h +++ b/drivers/net/ethernet/sfc/net_driver.h @@ -468,24 +468,11 @@ enum nic_state { }; /* - * Alignment of page-allocated RX buffers - * - * Controls the number of bytes inserted at the start of an RX buffer. - * This is the equivalent of NET_IP_ALIGN [which controls the alignment - * of the skb->head for hardware DMA]. - */ -#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS -#define EFX_PAGE_IP_ALIGN 0 -#else -#define EFX_PAGE_IP_ALIGN NET_IP_ALIGN -#endif - -/* * Alignment of the skb->head which wraps a page-allocated RX buffer * * The skb allocated to wrap an rx_buffer can have this alignment. Since * the data is memcpy'd from the rx_buf, it does not need to be equal to - * EFX_PAGE_IP_ALIGN. + * NET_IP_ALIGN. */ #define EFX_PAGE_SKB_ALIGN 2 diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c index e73e30b..99f70dd 100644 --- a/drivers/net/ethernet/sfc/rx.c +++ b/drivers/net/ethernet/sfc/rx.c @@ -93,7 +93,7 @@ static inline void efx_sync_rx_buffer(struct efx_nic *efx, void efx_rx_config_page_split(struct efx_nic *efx) { - efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + EFX_PAGE_IP_ALIGN, + efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + NET_IP_ALIGN, L1_CACHE_BYTES); efx->rx_bufs_per_page = efx->rx_buffer_order ? 1 : ((PAGE_SIZE - sizeof(struct efx_rx_page_state)) / @@ -188,9 +188,9 @@ static int efx_init_rx_buffers(struct efx_rx_queue *rx_queue) do { index = rx_queue->added_count & rx_queue->ptr_mask; rx_buf = efx_rx_buffer(rx_queue, index); - rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN; + rx_buf->dma_addr = dma_addr + NET_IP_ALIGN; rx_buf->page = page; - rx_buf->page_offset = page_offset + EFX_PAGE_IP_ALIGN; + rx_buf->page_offset = page_offset + NET_IP_ALIGN; rx_buf->len = efx->rx_dma_len; rx_buf->flags = 0; ++rx_queue->added_count;
The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no need for this optimisation any more. Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> --- drivers/net/ethernet/sfc/efx.c | 4 ++-- drivers/net/ethernet/sfc/net_driver.h | 15 +-------------- drivers/net/ethernet/sfc/rx.c | 6 +++--- 3 files changed, 6 insertions(+), 19 deletions(-)