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authorBen Hutchings <bhutchings@solarflare.com>2011-02-22 17:26:10 +0000
committerBen Hutchings <bhutchings@solarflare.com>2011-03-04 17:58:42 +0000
commit65f0b417dee94f779ce9b77102b7d73c93723b39 (patch)
tree390279203a8c73a986d15be5cc30f9bb2e95c1e8 /drivers/net/sfc
parent6d84b986b26bac1d4d678ff10c10a633bf53f834 (diff)
sfc: Use write-combining to reduce TX latency
Based on work by Neil Turton <nturton@solarflare.com> and Kieran Mansley <kmansley@solarflare.com>. 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 <bhutchings@solarflare.com>
Diffstat (limited to 'drivers/net/sfc')
-rw-r--r--drivers/net/sfc/efx.c4
-rw-r--r--drivers/net/sfc/io.h13
-rw-r--r--drivers/net/sfc/mcdi.c9
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)