On m68k, where the alignment of 32-bit words is 2 bytes: net/openvswitch/flow.c:1984:2: error: call to '__compiletime_assert_1984' declared with attribute error: BUILD_BUG_ON failed: sizeof(struct sw_flow_key) % sizeof(long) (http://kisskb.ellerman.id.au/kisskb/buildresult/9422860/) This was introduced by commit 5828cd9a68873df1340b420371c02c47647878fb Author: Andy Zhou <azhou@xxxxxxxxxx> Date: Tue Aug 27 13:02:21 2013 -0700 openvswitch: optimize flow compare and mask functions Make sure the sw_flow_key structure and valid mask boundaries are always machine word aligned. Optimize the flow compare and mask operations using machine word size operations. This patch improves throughput on average by 15% when CPU is the bottleneck of forwarding packets. This patch is inspired by ideas and code from a patch submitted by Peter Klausler titled "replace memcmp() with specialized comparator". However, The original patch only optimizes for architectures support unaligned machine word access. This patch optimizes for all architectures. A quick fix to satisfy the build check is to make the padding explicit (gmail-whitespace-damaged diff): diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h index b65f885..15f08d9 100644 --- a/net/openvswitch/flow.h +++ b/net/openvswitch/flow.h @@ -78,6 +78,7 @@ struct sw_flow_key { u32 priority; /* Packet QoS priority. */ u32 skb_mark; /* SKB mark. */ u16 in_port; /* Input switch port (or DP_MAX_PORTS). + u16 pad; } phy; struct { u8 src[ETH_ALEN]; /* Ethernet source address. */ However, I have some doubts about other alignment "enforcements": "__aligned(__alignof__(long))" makes the whole struct aligned to the alignment rule for "long": 1. This is only 2 bytes on m68k, i.e. != sizeof(long). 2. This is 4 bytes on many 32-bit platforms, which may be less than the default alignment for "__be64" (cfr. some members of struct ovs_key_ipv4_tunnel), so this may make those 64-bit members unaligned. I guess you want (at least) 4 byte alignment on 32-bit, and prefer 8 byte alignment on 64-bit? Not specifying any alignment constraint will give you most of that (except on 64-bit platforms where 64-bit words must be only 4-byte aligned). There's another build check "BUILD_BUG_ON(sizeof(long) % sizeof(u32))". Isn't this always true on Linux, as "long" is never smaller than 4 bytes? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
