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| author | Ben Hutchings <bhutchings@solarflare.com> | 2011-02-22 17:26:10 +0000 |
|---|---|---|
| committer | Ben Hutchings <bhutchings@solarflare.com> | 2011-03-04 17:58:42 +0000 |
| commit | 65f0b417dee94f779ce9b77102b7d73c93723b39 (patch) | |
| tree | 390279203a8c73a986d15be5cc30f9bb2e95c1e8 /drivers/net/sfc/io.h | |
| parent | 6d84b986b26bac1d4d678ff10c10a633bf53f834 (diff) | |
| download | op-kernel-dev-65f0b417dee94f779ce9b77102b7d73c93723b39.zip op-kernel-dev-65f0b417dee94f779ce9b77102b7d73c93723b39.tar.gz | |
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/io.h')
| -rw-r--r-- | drivers/net/sfc/io.h | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/drivers/net/sfc/io.h b/drivers/net/sfc/io.h index dc45110..d9d8c2e 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, \ |
