Date: Tue, 21 Aug 2012 08:31:00 -0600 From: Warner Losh <imp@bsdimp.com> To: Marius Strobl <marius@alchemy.franken.de> Cc: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>, freebsd-net@freebsd.org, Mitya <mitya@cabletv.dp.ua>, freebsd-hackers@freebsd.org Subject: Re: Replace bcopy() to update ether_addr Message-ID: <92186FE4-F83A-43A2-B1C9-85A1C42513AC@bsdimp.com> In-Reply-To: <20120821112655.GA90066@alchemy.franken.de> References: <50324DB4.6080905@cabletv.dp.ua> <alpine.BSF.2.00.1208201844220.35173@wojtek.tensor.gdynia.pl> <B2BB7724-57A9-40C9-AE9F-FFEC83D9DE9A@bsdimp.com> <alpine.BSF.2.00.1208202117230.19372@wojtek.tensor.gdynia.pl> <5452BF37-3658-4C1F-B965-CE3EA28B6EA5@bsdimp.com> <20120821112655.GA90066@alchemy.franken.de>
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On Aug 21, 2012, at 5:26 AM, Marius Strobl wrote: > On Mon, Aug 20, 2012 at 01:20:29PM -0600, Warner Losh wrote: >>=20 >> On Aug 20, 2012, at 1:17 PM, Wojciech Puchar wrote: >>=20 >>>>> or use ++. >>>>>=20 >>>>> i think it is always aligned to 2 bytes and this should produce = usable code on any CPU? should be 6 instructions on MIPS and PPC IMHO. >>>>=20 >>>> We should tag it as __aligned(2) then, no? If so, then the = compiler should generate the code you posted. >>> should is the most important word in Your post. what it actually do = - i don't know. >>=20 >> If we are requiring this to be __aligned(2), we should tag it as such = to enforce this. >>=20 >> Even without this tagging, the code to do a structure level copy of 6 = bytes is going to be tiny... >>=20 >=20 > While the __aligned(2) approach certainly works, I've actually rather > mixed experiences on x86 with it as the compiler doesn't necessarily > produce the small and efficient one would expect from code it. Such > a change certainly shouldn't be done just on the assumption that the > compiler has all hints required to produce good code from it but the > resulting asm should be verified across all affected architectures. Very true... I would have thought that went without saying... Warner=
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