Date: Wed, 25 Aug 1999 15:10:03 -0700 (PDT) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/11736: On fast machines kernel reports negative i586_bzero bandwith values due to datatype overflow Message-ID: <199908252210.PAA34411@freefall.freebsd.org>
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The following reply was made to PR kern/11736; it has been noted by GNATS.
From: Bruce Evans <bde@zeta.org.au>
To: bde@freebsd.org, freebsd-gnats-submit@freebsd.org,
sobomax@altavista.net
Cc:
Subject: Re: kern/11736: On fast machines kernel reports negative i586_bzero bandwith values due to datatype overflow
Date: Thu, 26 Aug 1999 08:01:11 +1000
>It seems that all OK now, so you can close this PR.
I don't think I actually fixed it. The problem is that the test is
run before interrupts are enabled, so the i8254 clock overflows
after 10 msec. I fixed overflow detection, so the clock is accurate
for up to 20 msec depending on when the test is started. The test
writes 10^6 bytes which normally takes 5-10 msec on a P5 (it takes
about 6 msec on my P5/133). However, K6-1's at least are slower
(the test takes about 12 msec on my K6-1/233), so there is some
chance of it not working.
Possible fixes:
1) always use the TSC for timing the test.
2) use a smaller buffer and be more careful about caching. The test
should be more careful about caching anyway.
Bruce
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