| Message ID | 1368482482.3305.50.camel@bwh-desktop.uk.solarflarecom.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Tue, May 14, 2013 at 12:01 AM, Ben Hutchings <bhutchings@solarflare.com> wrote: > efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus > a software structure, each appropriately aligned, into a single page. > Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case > on s390, this assertion fails. > > The current scatter buffer size is also not a multiple of 64 or 128, > which are more common cache line sizes. If we can make both the start > and end of a scatter buffer cache-aligned, this will reduce the need > for read-modify-write operations on inter- processor links. > > Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 == > 1792. (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE > also affects user-level networking where a larger amount of > housekeeping data may be needed. Although this version of the driver > does not support user-level networking, I prefer to keep scattering > behaviour consistent with the out-of-tree version.) > > This still doesn't fix the s390 build because like most architectures > it has NET_IP_ALIGN == 2. When NET_IP_ALIGN != 0 we cannot achieve > cache line alignment at either the start or end of a scatter buffer, > so there is actually no point in padding the buffers to a multiple of > the cache line size. All we need is 4-byte alignment of the network > header, so do that. > > Adjust the assertions accordingly. > > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> > Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com> > Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> Fixes the s390 build, so Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- 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
From: Ben Hutchings <bhutchings@solarflare.com> Date: Mon, 13 May 2013 23:01:22 +0100 > efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus > a software structure, each appropriately aligned, into a single page. > Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case > on s390, this assertion fails. > > The current scatter buffer size is also not a multiple of 64 or 128, > which are more common cache line sizes. If we can make both the start > and end of a scatter buffer cache-aligned, this will reduce the need > for read-modify-write operations on inter- processor links. > > Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 == > 1792. (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE > also affects user-level networking where a larger amount of > housekeeping data may be needed. Although this version of the driver > does not support user-level networking, I prefer to keep scattering > behaviour consistent with the out-of-tree version.) > > This still doesn't fix the s390 build because like most architectures > it has NET_IP_ALIGN == 2. When NET_IP_ALIGN != 0 we cannot achieve > cache line alignment at either the start or end of a scatter buffer, > so there is actually no point in padding the buffers to a multiple of > the cache line size. All we need is 4-byte alignment of the network > header, so do that. > > Adjust the assertions accordingly. > > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> > Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com> > 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
On Mon, 2013-05-13 at 23:01 +0100, Ben Hutchings wrote: [...] > This still doesn't fix the s390 build because like most architectures > it has NET_IP_ALIGN == 2. When NET_IP_ALIGN != 0 we cannot achieve > cache line alignment at either the start or end of a scatter buffer, > so there is actually no point in padding the buffers to a multiple of > the cache line size. All we need is 4-byte alignment of the network > header, so do that. [...] I was just thinking about this again. Do we need to care about alignment in a page fragment at all? Won't all the headers be pulled into the header area before being accessed with any instructions that would require alignment? (We aren't using build_skb().) Ben.
diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c index 999289b..39e4cb3 100644 --- a/drivers/net/ethernet/sfc/efx.c +++ b/drivers/net/ethernet/sfc/efx.c @@ -643,9 +643,11 @@ static void efx_start_datapath(struct efx_nic *efx) efx->rx_scatter = false; efx->rx_buffer_order = 0; } else if (efx->type->can_rx_scatter) { + BUILD_BUG_ON(EFX_RX_USR_BUF_SIZE % L1_CACHE_BYTES); BUILD_BUG_ON(sizeof(struct efx_rx_page_state) + - NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE > - PAGE_SIZE / 2); + 2 * ALIGN(NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE, + EFX_RX_BUF_ALIGNMENT) > + PAGE_SIZE); efx->rx_scatter = true; efx->rx_dma_len = EFX_RX_USR_BUF_SIZE; efx->rx_buffer_order = 0; diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h index 5efddf3..39d6bd77 100644 --- a/drivers/net/ethernet/sfc/net_driver.h +++ b/drivers/net/ethernet/sfc/net_driver.h @@ -72,8 +72,20 @@ /* Maximum possible MTU the driver supports */ #define EFX_MAX_MTU (9 * 1024) -/* Size of an RX scatter buffer. Small enough to pack 2 into a 4K page. */ -#define EFX_RX_USR_BUF_SIZE 1824 +/* Size of an RX scatter buffer. Small enough to pack 2 into a 4K page, + * and should be a multiple of the cache line size. + */ +#define EFX_RX_USR_BUF_SIZE (2048 - 256) + +/* If possible, we should ensure cache line alignment at start and end + * of every buffer. Otherwise, we just need to ensure 4-byte + * alignment of the network header. + */ +#if NET_IP_ALIGN == 0 +#define EFX_RX_BUF_ALIGNMENT L1_CACHE_BYTES +#else +#define EFX_RX_BUF_ALIGNMENT 4 +#endif /* Forward declare Precision Time Protocol (PTP) support structure. */ struct efx_ptp_data; diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c index 99f70dd..a7dfe36 100644 --- a/drivers/net/ethernet/sfc/rx.c +++ b/drivers/net/ethernet/sfc/rx.c @@ -94,7 +94,7 @@ 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 + NET_IP_ALIGN, - L1_CACHE_BYTES); + EFX_RX_BUF_ALIGNMENT); efx->rx_bufs_per_page = efx->rx_buffer_order ? 1 : ((PAGE_SIZE - sizeof(struct efx_rx_page_state)) / efx->rx_page_buf_step);
efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus a software structure, each appropriately aligned, into a single page. Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case on s390, this assertion fails. The current scatter buffer size is also not a multiple of 64 or 128, which are more common cache line sizes. If we can make both the start and end of a scatter buffer cache-aligned, this will reduce the need for read-modify-write operations on inter- processor links. Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 == 1792. (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE also affects user-level networking where a larger amount of housekeeping data may be needed. Although this version of the driver does not support user-level networking, I prefer to keep scattering behaviour consistent with the out-of-tree version.) This still doesn't fix the s390 build because like most architectures it has NET_IP_ALIGN == 2. When NET_IP_ALIGN != 0 we cannot achieve cache line alignment at either the start or end of a scatter buffer, so there is actually no point in padding the buffers to a multiple of the cache line size. All we need is 4-byte alignment of the network header, so do that. Adjust the assertions accordingly. Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> --- drivers/net/ethernet/sfc/efx.c | 6 ++++-- drivers/net/ethernet/sfc/net_driver.h | 16 ++++++++++++++-- drivers/net/ethernet/sfc/rx.c | 2 +- 3 files changed, 19 insertions(+), 5 deletions(-)