Date: Thu, 31 Jul 1997 03:35:52 +1000 From: Bruce Evans <bde@zeta.org.au> To: cgull@smoke.marlboro.vt.us, sos@sos.freebsd.dk Cc: freebsd-current@FreeBSD.ORG, se@FreeBSD.ORG Subject: Re: code talks: announcing EIDE bus master patches Message-ID: <199707301735.DAA26172@godzilla.zeta.org.au>
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>Well, bonnie reports an increase in CPU load and some increase in I/O >speed on the hack box I developed the code on, while a little >spin-loop-at-idle-priority hack i coded up shows an improvement in >available CPU that it can consume. My conclusion: bonnie's CPU load >numbers are useless, at least for IDE drives. Bonnie doesn't report interrupt overhead. FreeBSD does too good a job of separating interrupt overhead from syscall overhead, and there is no system call for reporting the interrupt overhead. The overhead is easy to see using `systat -vmstat' and easy to account for provided there is only one process causing most of the interrupts (the time for a few hundred normal interrupts is insignificant except on slow machines). This is the same setup as is required for the spinloop method. Bonnie's CPU load numbers are also fairly useless for SCSI drives :-). They measure mainly the driver, filesystem and buffer cache overheads. DMA overhead is hard to measure, but the spinloop method works well for giving the total overhead. Bruce
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