From: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> > Reported-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> > Signed-off-by: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx> Applied. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
