From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Jarzmik Subject: Re: [PATCH 2/3] ARM: convert to generated system call tables Date: Wed, 26 Oct 2016 22:14:46 +0200 Message-ID: <87vawe27gp.fsf@belgarion.home> References: <4337157.Eff9E2riVH@wuerfel> <20161021154856.GC1041@n2100.armlinux.org.uk> <24632117.YsmPs86ri6@wuerfel> <87eg382kv9.fsf@belgarion.home> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: (Geert Uytterhoeven's message of "Mon, 24 Oct 2016 11:25:03 +0200") Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Geert Uytterhoeven Cc: Arnd Bergmann , Russell King - ARM Linux , linux-arch , linux-api , "linux-arm-kernel@lists.infradead.org" List-Id: linux-api@vger.kernel.org Geert Uytterhoeven writes: > On Sat, Oct 22, 2016 at 10:23 PM, Robert Jarzmik wrote: >> Arnd Bergmann writes: >> >>> On Friday, October 21, 2016 4:48:56 PM CEST Russell King - ARM Linux wrote: >>>> What's the point of the x32 mode? >>> >>> On x86, the motivation is faster code for most use cases that >>> don't need a lot of memory, as the 64-bit opcodes have 16 registers >>> rather than 8 in 32-bit mode but 32-bit pointers have lower >>> cache footprint than 64-bit pointers. >> >> For completness, the second point of x32 AFAIU is the IP-relative addressing >> which is not available in standard 32 bit mode, which improves PIC code. For >> simple not algorithmic code (think Android HAL for example) with many shared >> libraries, it's better in the Hardware Abstraction Layer Libraries, instead of >> the push-to-stack and pop register. > > But that's not an advantage compared to full am64 mode, right? Nope, the amd64 (that's what you have in mind with am64, not aarch64 right ?) mode has the IP-relative has well, so x32 has no advantage over amd64 in this area. x32 over amd64 advantage is cache and memory footprint AFAICT, I don't see other benefits. There doesn't seem to be any ISA differences, or I didn't really notice in my daily system performance analysis job. There was a nice presentation made by Peter Anvin at a Plumber conference, here : http://linuxplumbersconf.org/2011/ocw/sessions/531 Cheers. -- Robert