Date: Thu, 17 Jun 1999 15:16:46 -0500 (EST) From: Alfred Perlstein <bright@rush.net> To: mike@hyperreal.org Cc: questions@freebsd.org Subject: Re: Optimizing IDE performance revisited Message-ID: <Pine.BSF.3.96.990617151259.14320q-100000@cygnus.rush.net> In-Reply-To: <19990617172206.21155.qmail@hyperreal.org>
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On Thu, 17 Jun 1999 mike@hyperreal.org wrote: > Alfred Perlstein wrote: > > Enabling PIO or DMA doesn't do all that much for transfer rate, however > > it offloads a lot of work from the CPU. > > > > Before I enabled DMA on my boxes, during heavy compiles top showed > > about 50% or more CPU devoted to "interupt" (processing hardware IO) > > when i switched to DMA it went to under 1% :) > > > > PIO probably isn't as drastic, but can probably spare you mucho cycles. > > I've already enabled PIO mode 3 in the BIOS, and there are no options to enable > any kind of DMA (this is a 1994ish on-board PCI IDE controller). > > Is there something else that I need to configure in the kernel to enable PIO > or DMA? yes, set your IDE flags to 0xa0ffa0ff , or some subset of that, check the LINT kernel config file, some machines that don't support DMA will hang if DMA is enabled, so double check it. > > if you want to see raw read performance try this: > > dd if=/dev/rwd0 of=/dev/null bs=512 count=1000 > > How do I interpret the results? simply, just compare the before and after, before you enabled PIO/dma and after you enabled it, you should see a gain in transfer speed, or a decrease in CPU utilization (you can monitor it via the "top" command) unless there is a specific reason not to, please "cc" all questions to the list it orginiated on, we don't want to deprive people of what we re learning do we? :) -Alfred To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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