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
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