Date: Wed, 19 Feb 1997 20:59:14 +0100 From: se@freebsd.org (Stefan Esser) To: msmith@atrad.adelaide.edu.au (Michael Smith) Cc: se@freebsd.org (Stefan Esser), hardware@freebsd.org Subject: Re: _big_ IDE disks? Message-ID: <19970219205914.RB27571@x14.mi.uni-koeln.de> In-Reply-To: <199702140035.LAA21975@genesis.atrad.adelaide.edu.au>; from Michael Smith on Feb 14, 1997 11:05:39 %2B1030 References: <19970213175603.JR15968@x14.mi.uni-koeln.de> <199702140035.LAA21975@genesis.atrad.adelaide.edu.au>
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On Feb 14, msmith@atrad.adelaide.edu.au (Michael Smith) wrote: > wdc0 at 0x1f0-0x1f7 irq 14 flags 0x80ff80ff on isa > wdc0: unit 0 (wd0): <Maxtor 85120 A8 ->, 32-bit, multi-block-16 > wd0: 788MB (10003392 sectors), 9924 cyls, 16 heads, 63 S/T, 512 B/S > IOZONE performance measurements: > 8339742 bytes/second for writing the file > 9316631 bytes/second for reading the file > > -------Sequential Output-------- ---Sequential Input-- --Random-- > -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks--- > Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU > 128 3858 71.8 8178 28.2 2486 14.1 4210 71.1 8280 28.1 117.0 4.7 Ok. Quite good performance for an (E)IDE drive ... Bruce Evans recently pointed out, that the CPU% load actually is 100%, but the cycles not accounted for are spent in the WD driver's interrupt handler. This indicates, that 30% of a P5-166 is required for 4MB/s, or that the CPU overhead for the PIO mode transfer is some 8% of the P5-166 per MB/s ... The 8MB/s on block transfers should thus correspond to some 65%CPU spent in the interrupt handler, which would mean, that the CPU is near 100% busy doing these transfers (while there would be some 70% of the CPU left for other processes, if the disk was driven by a bus-master controller.) > (Just for amusement, I ran iozone without any of the go-faster options > for the 'wd' driver enabled : > > Writing the 128 Megabyte file, 'iozone.tmp'...22.453125 seconds > Reading the file...23.945312 seconds > > IOZONE performance measurements: > 5977685 bytes/second for writing the file > 5605177 bytes/second for reading the file > > .... so they definitely help 8) We really should be able to compare with a bus-master EIDE driver. The PIIX3 docs (available from Intel's WWW server as a PDF file) give enough detail, to implement DMA transfers for that chip IMHO, so somebody should go for it ... Regards, STefan
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