Date: Mon, 23 Dec 2013 11:45:47 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Luigi Rizzo <rizzo@iet.unipi.it>, current@freebsd.org Subject: Re: RFC can we use __builtin_prefetch() directly in our kernel sources ? Message-ID: <201312231145.47679.jhb@freebsd.org> In-Reply-To: <20131216165014.GA15126@onelab2.iet.unipi.it> References: <20131216165014.GA15126@onelab2.iet.unipi.it>
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On Monday, December 16, 2013 11:50:14 am Luigi Rizzo wrote: > Is it ok in kernel code to use __builtin_prefetch() and assume that > all supported compilers will do the right thing for all architectures ? > > I am asking is because I need to use prefetch() in a small number > of places in my netmap code, and nothing in our kernel sources uses > __builtin_prefetch() directly. In the (very few, mostly 10G drivers) > cases where prefetch() is used the drivers redefine the function > themselves as some inline asm() or an empty > > #define prefetch(x) > > This also happens in many places in the linux kernel, for what matters > (relevant because hte netmap kernel code also needs to compile there). > > Anyways, so far in the netmap code i have followed the established > practice but my (re)definition of prefetch() in netmap_kern.h > clashes with some in the individual drivers, so I'd rather > find a better way. Hmmmm, have you considered using a 'netmap_prefetch' macro or the like? You can likely just use __builtin_prefetch() on FreeBSD I think, but that might also let you avoid collisions on Linux as well. I think you can use __builtin_prefetch(), I'm just not sure, and it's kind of ugly to see __builtin_*() in code directly IMHO. -- John Baldwin
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