Date: Mon, 20 Aug 2012 10:41:15 -0600 From: Warner Losh <imp@bsdimp.com> To: Mitya <mitya@cabletv.dp.ua> Cc: freebsd-hackers@freebsd.org, freebsd-net@freebsd.org Subject: Re: Replace bcopy() to update ether_addr Message-ID: <4C06696D-EF17-411D-A229-B738B9D47B8A@bsdimp.com> In-Reply-To: <50324DB4.6080905@cabletv.dp.ua> References: <50324DB4.6080905@cabletv.dp.ua>
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On Aug 20, 2012, at 8:46 AM, Mitya wrote: > Hi. > I found some overhead code in /src/sys/net/if_ethersubr.c and = /src/sys/netgraph/ng_ether.c >=20 > It contains strings, like bcopy(src, dst, ETHER_ADDR_LEN); > When src and dst are "struct ether_addr*", and ETHER_ADDR_LEN equal 6. > This code call every time, when we send Ethernet packet. > On example, on my machine in invoked nearly 20K per second. >=20 > Why we are use bcopy(), to copy only 6 bytes? > Answer - in some architectures we are can not directly copy unaligned = data. True for shorts, longs, etc. But why do we need it for ether_addr? It = is a struct that's just an array... That's always safe. > I propose this solution. >=20 > In file /usr/src/include/net/ethernet.h add this lines: >=20 > static inline void ether_addr_copy(ether_addr* src, ether_addr* dst) { > #if defined(__i386__) || defined(__amd64__) Bleck. that's uber ugly. We have a define for unaligned vs aligned = architectures. we should use that here. If we even need this ifdef at = all. Warner > *dst =3D *src; > #else > bcopy(src, dst, ETHER_ADDR_LEN); > #endif > } >=20 > On platform i386 gcc produce like this code: > leal -30(%ebp), %eax > leal 6(%eax), %ecx > leal -44(%ebp), %edx > movl (%edx), %eax > movl %eax, (%ecx) > movzwl 4(%edx), %eax > movw %ax, 4(%ecx) > And clang produce this: > movl -48(%ebp), %ecx > movl %ecx, -26(%ebp) > movw -44(%ebp), %si > movw %si, -22(%ebp) >=20 >=20 > All this variants are much faster, than bcopy() >=20 > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to = "freebsd-hackers-unsubscribe@freebsd.org"
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