Date: Wed, 29 Oct 2003 14:24:58 -0800 From: "David Schwartz" <davids@webmaster.com> To: "Bill Moran" <wmoran@potentialtech.com> Cc: "Chat@Freebsd. Org" <chat@freebsd.org> Subject: RE: How much better are 64 but platforms Message-ID: <MDEHLPKNGKAHNMBLJOLKAENPHIAA.davids@webmaster.com> In-Reply-To: <3FA00634.6000002@potentialtech.com>
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> I've never used FreeBSD on a 64 bit platform, and with a recent > project I've got > a client asking me, "How much faster would this run if we put it > on an Itanium." > > So, in the future, I'll probably be getting a 64 bit machine to > try this out on. > > But it got me thinking, what should I _expect_ to see in > improvement? This > application is mostly comparing strings, there are no 64 bit > integers or floats > to be obvious bottlenecks on a 32 bit platform, so (lacking > actual experience) > how much can I expect the application to speed up if I move it to a 64 bit > platform? Applications that primarily manipulate strings are not faster on 64-bit platforms and, in some cases, run more slowly. We suspect this is because, in relative terms, single byte accesses are more expensive. Applications that manipulate small integers (that fit in 32-bits) generally run at about the same speed. We do see slight slowdowns simply because of extra memory bandwidth being used due to 64-bits values taking twice as much space on the bus as 32. Applications that deal with large numbers (like cryptography) or bulk data (like compression) tend to get a boost. Database applications generally do get a performance boost because of the better ability to deal with large amounts of memory. In previous steps, 8-bit to 16-bit and 16-bit to 32-bit, quantities that previously had to be manipulated as multiple units could now be handled as a single unit. Most counters and integers exceed 8-bits, to moving to 16-bits halved the work for almost anything. Still, many such things didn't fit in 16-bits, so 32-bits halved the work for many things. However, almost everything fits in 32-bits. So 64-bits either gets no benefit for most things or just results in dragging extra bytes across the memory bus, which doesn't get any faster. However, we'll all need to smoothly handle more than 4Gb of memory real soon now. Memory mapping an 8Gb database may speed things up as well. It's too early for me to tell about these kinds of things yet. DS
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