Date: Fri, 7 Apr 2006 05:29:50 +1000 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Pete French <petefrench@ticketswitch.com> Cc: freebsd-stable@freebsd.org Subject: Re: Pros and Cons of amd64 (versus i386). Message-ID: <20060406192950.GE700@turion.vk2pj.dyndns.org> In-Reply-To: <E1FRVcq-0004pJ-4c@dilbert.firstcallgroup.co.uk> References: <CBC0AAB4-EC80-44C8-BCCE-010DE99D4BC0@khera.org> <E1FRVcq-0004pJ-4c@dilbert.firstcallgroup.co.uk>
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On Thu, 2006-Apr-06 15:38:20 +0100, Pete French wrote: >I was thinking of moving this to amd64, but was kind of put off by results >from a test system I setup using an Athlon 64 3700+ to talk to this >machine. The opteron box is currently running 6.1-PRE/i386, and the 3700 is >runiing either Windows XP or 61-PRE/amd64. Under Windows I can completely >saturate the ether comming in, and get 70% bandwidth going out (it's gig >ether). Under amd64 on the client end I can only get about 55% utilisation >in both directions. This surprised me a lot as when I was running i386 >on that box it was always faster. Of course a number of variables have >changed since then (primarily moving from a broadcom gigabit card to using >the onboard realtek card), but I was concened that the difference was due to >the 64 bit operating system, as opposed to superior windws drivers, which >seemed unlikely! If you want to do a valid benchmark, you really need to use the same hardware for the testing. amd64 is not necessarily faster than i386 on the same hardware: On the downside: - amd64 has more, larger registers so context switching is slower - 64-bit long/pointer and lower code density means larger working set size and lower cache effectiveness On the upside: - more registers means less register spills (better code) - I think there's more efficient support for PIC code - 64-bit arithmetic means faster multi-precision math (think RSA/DSA/SSL) - access to >2GB virtual address space >I know that what I should do is install i386 on the client and test again, but >doing that will lose my only 64 bit environment so I am loathe to do so. Any >comments ? Backup your amd64 environment and install i386. You can re-install the amd64 once the testing is finished. The best benchmark is always your own application. -- Peter Jeremy
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