From 65f0b417dee94f779ce9b77102b7d73c93723b39 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Tue, 22 Feb 2011 17:26:10 +0000 Subject: [PATCH] sfc: Use write-combining to reduce TX latency Based on work by Neil Turton and Kieran Mansley . The BIU has now been verified to handle 3- and 4-dword writes within a single 128-bit register correctly. This means we can enable write- combining and only insert write barriers between writes to distinct registers. This has been observed to save about 0.5 us when pushing a TX descriptor to an empty TX queue. Signed-off-by: Ben Hutchings --- drivers/net/sfc/efx.c | 4 ++-- drivers/net/sfc/io.h | 13 +++++++++---- drivers/net/sfc/mcdi.c | 9 +++++---- 3 files changed, 16 insertions(+), 10 deletions(-) diff --git a/drivers/net/sfc/efx.c b/drivers/net/sfc/efx.c index d563049859a8..b8bd936374f2 100644 --- a/drivers/net/sfc/efx.c +++ b/drivers/net/sfc/efx.c @@ -1104,8 +1104,8 @@ static int efx_init_io(struct efx_nic *efx) rc = -EIO; goto fail3; } - efx->membase = ioremap_nocache(efx->membase_phys, - efx->type->mem_map_size); + efx->membase = ioremap_wc(efx->membase_phys, + efx->type->mem_map_size); if (!efx->membase) { netif_err(efx, probe, efx->net_dev, "could not map memory BAR at %llx+%x\n", diff --git a/drivers/net/sfc/io.h b/drivers/net/sfc/io.h index dc45110b2456..d9d8c2ef1074 100644 --- a/drivers/net/sfc/io.h +++ b/drivers/net/sfc/io.h @@ -48,9 +48,9 @@ * replacing the low 96 bits with zero does not affect functionality. * - If the host writes to the last dword address of such a register * (i.e. the high 32 bits) the underlying register will always be - * written. If the collector does not hold values for the low 96 - * bits of the register, they will be written as zero. Writing to - * the last qword does not have this effect and must not be done. + * written. If the collector and the current write together do not + * provide values for all 128 bits of the register, the low 96 bits + * will be written as zero. * - If the host writes to the address of any other part of such a * register while the collector already holds values for some other * register, the write is discarded and the collector maintains its @@ -103,6 +103,7 @@ static inline void efx_writeo(struct efx_nic *efx, efx_oword_t *value, _efx_writed(efx, value->u32[2], reg + 8); _efx_writed(efx, value->u32[3], reg + 12); #endif + wmb(); mmiowb(); spin_unlock_irqrestore(&efx->biu_lock, flags); } @@ -125,6 +126,7 @@ static inline void efx_sram_writeq(struct efx_nic *efx, void __iomem *membase, __raw_writel((__force u32)value->u32[0], membase + addr); __raw_writel((__force u32)value->u32[1], membase + addr + 4); #endif + wmb(); mmiowb(); spin_unlock_irqrestore(&efx->biu_lock, flags); } @@ -139,6 +141,7 @@ static inline void efx_writed(struct efx_nic *efx, efx_dword_t *value, /* No lock required */ _efx_writed(efx, value->u32[0], reg); + wmb(); } /* Read a 128-bit CSR, locking as appropriate. */ @@ -237,12 +240,14 @@ static inline void _efx_writeo_page(struct efx_nic *efx, efx_oword_t *value, #ifdef EFX_USE_QWORD_IO _efx_writeq(efx, value->u64[0], reg + 0); + _efx_writeq(efx, value->u64[1], reg + 8); #else _efx_writed(efx, value->u32[0], reg + 0); _efx_writed(efx, value->u32[1], reg + 4); -#endif _efx_writed(efx, value->u32[2], reg + 8); _efx_writed(efx, value->u32[3], reg + 12); +#endif + wmb(); } #define efx_writeo_page(efx, value, reg, page) \ _efx_writeo_page(efx, value, \ diff --git a/drivers/net/sfc/mcdi.c b/drivers/net/sfc/mcdi.c index 8bba8955f310..5e118f0d2479 100644 --- a/drivers/net/sfc/mcdi.c +++ b/drivers/net/sfc/mcdi.c @@ -94,14 +94,15 @@ static void efx_mcdi_copyin(struct efx_nic *efx, unsigned cmd, efx_writed(efx, &hdr, pdu); - for (i = 0; i < inlen; i += 4) + for (i = 0; i < inlen; i += 4) { _efx_writed(efx, *((__le32 *)(inbuf + i)), pdu + 4 + i); - - /* Ensure the payload is written out before the header */ - wmb(); + /* use wmb() within loop to inhibit write combining */ + wmb(); + } /* ring the doorbell with a distinctive value */ _efx_writed(efx, (__force __le32) 0x45789abc, doorbell); + wmb(); } static void efx_mcdi_copyout(struct efx_nic *efx, u8 *outbuf, size_t outlen) -- 2.11.0