Date: Mon, 17 Apr 1995 17:55:58 -0400 From: Michael Vernick <vernick@cs.sunysb.edu> To: freebsd-scsi@FreeBSD.org Subject: SCSI command processing Message-ID: <199504172155.RAA29886@cs.sunysb.edu>
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I have also done some testing of SCSI overhead processing. On average an 'Inquiry' command sent to the disk over an EISA bus takes 1.2 ms, that is going in and out of user space from start to finish. To retrieve 1 block from the disk cache also takes about the same amount of time, 1.22ms on average. I test this by first doing a read of a random block and then re-read it. The first read incurs the seek, rotation, and transfer overhead, the second read is satisfied by from the disk cache. So the 1.22 ms includes: going in and out of user space, 2 each of: EISA bus transfer, SCSI controller overhead, SCSI bus transfer and disk overhead. Thus, it would seem the disk overhead is quite small. mv
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