diff options
| 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/mcdi.c | |
| parent | 6d84b986b26bac1d4d678ff10c10a633bf53f834 (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/mcdi.c')
| -rw-r--r-- | drivers/net/sfc/mcdi.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/drivers/net/sfc/mcdi.c b/drivers/net/sfc/mcdi.c index 8bba8955f31..5e118f0d247 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) |