Date: Fri, 30 May 1997 02:36:44 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, phk@dk.tfs.com Cc: current@freebsd.org Subject: Re: disk cache challenged by small block sizes Message-ID: <199705291636.CAA20635@godzilla.zeta.org.au>
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>>ufs with a block size of 4K was about the same speed as ext2fs with a block >>size of 4K. ufs with a block size of 8K was significantly (25%) slower. > =========================================================== > >Uhm, isn't that rather obvious ? No :-). >The chances of being able to do one DMA into two (physically) consecutive >pages are very very slim as far as I can tell, so you will generally get >better performance when you do it in page size chunks ? The pages are normally discontiguous, so they are normally done in page- size chunks. A block size of 8K should allow better disk scheduling. Read-ahead is based in the principle of sending even larger requests to the driver. These times for raw i/o show that the OS's cache is doing something right to get even 700K/sec. Speeds in bytes/sec for dd'ing 512 blocks to/from /dev/zero: block size read write 512 24940 24940 1024 49643 49642 2048 98336 98145 4096 191187 191186 8192 321249 321247 16384 518759 519419 32768 730492 732447 65536 894033 896461 Bruce
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