Date: Mon, 5 Mar 2001 17:38:24 -0600 (CST) From: Chris Dillon <cdillon@wolves.k12.mo.us> To: Matt Dillon <dillon@earth.backplane.com> Cc: "E.B. Dreger" <eddy+public+spam@noc.everquick.net>, <freebsd-hackers@FreeBSD.ORG> Subject: Re: Machines are getting too damn fast Message-ID: <Pine.BSF.4.32.0103051729350.84853-100000@mail.wolves.k12.mo.us> In-Reply-To: <200103052324.f25NOin45226@earth.backplane.com>
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On Mon, 5 Mar 2001, Matt Dillon wrote: > :throughput. For example, on the PIII-850 (116MHz FSB and SDRAM, its > :overclocked) here on my desk with 256KB L2 cache: > : > :dd if=/dev/zero of=/dev/null bs=512k count=4000 > :4000+0 records in > :4000+0 records out > :2097152000 bytes transferred in 8.229456 secs (254834825 bytes/sec) > : > :dd if=/dev/zero of=/dev/null bs=128k count=16000 > :16000+0 records in > :16000+0 records out > :2097152000 bytes transferred in 1.204001 secs (1741819224 bytes/sec) > : > :Now THAT is a significant difference. :-) > > Interesting. I get very different results with the 1.3 GHz P4. The > best I seem to get is 1.4 GBytes/sec. I'm not sure what the L2 cache > is on the box, but it's definitely a consumer model. > > dd if=/dev/zero of=/dev/null bs=512k count=4000 > 2097152000 bytes transferred in 2.363903 secs (887156520 bytes/sec) > > dd if=/dev/zero of=/dev/null bs=128k count=16000 > 2097152000 bytes transferred in 1.471046 secs (1425619621 bytes/sec) > > If I use lower block sizes the syscall overhead blows up the > performance (it gets lower rather then higher). So I figure I don't > have as much L2 as on your system. IIRC, Intel is using a very different caching method on the P4 from what we are used to on just about every other x86 processor we've seen. Well, I can't remember if the data cache has changed much, but the instruction cache has. I doubt the difference in instruction cache behaviour would make a difference here though. Hmm. I wonder if it makes any difference that I'm using -march=pentium -mcpu=pentium for my CFLAGS? Actually, the kernel I tested on might even be using -march/-mcpu=pentiumpro, since I only recently changed it to =pentium to allow me to do buildworlds for another Pentium-class machine. I did wonder the same thing a while back and did the same test with and without the optimizations, and with pentiumpro opts the big block size transfer rate went _down_ a little bit, which was odd. I didn't compare with L2-cache-friendly blocks, though. -- Chris Dillon - cdillon@wolves.k12.mo.us - cdillon@inter-linc.net FreeBSD: The fastest and most stable server OS on the planet. For IA32 and Alpha architectures. IA64, PPC, and ARM under development. http://www.freebsd.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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