Date: Mon, 22 Sep 1997 15:45:17 -0600 From: "Justin T. Gibbs" <gibbs@plutotech.com> To: Nate Williams <nate@mt.sri.com> Cc: "Justin T. Gibbs" <gibbs@plutotech.com>, Bruce Evans <bde@zeta.org.au>, current@freebsd.org Subject: Re: cvs commit: src/sys/conf files src/sys/dev/vx if_vx.c if_vxreg.h src/sys/i386/apm apm.c src/sys/i386/conf GENERIC files.i386 src/sys/i386/eisa 3c5x9.c aha1742.c aic7770.c bt74x.c eisaconf.c eisaconf.h if_fea.c if_vx_eisa.c src/sys/i386/i386 autoconf.c ... Message-ID: <199709222145.PAA03221@pluto.plutotech.com> In-Reply-To: Your message of "Mon, 22 Sep 1997 15:34:03 MDT." <199709222134.PAA03250@rocky.mt.sri.com>
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>> If we implement high resolution timers, we will probably pay the O(hash >> chain length) insertion sort price in timeout and schedule a one shot >> timer for the next event that needs to run meaning that softclock is no >> longer tied to hz. > >Then, why implement the darn thing at all, when we could simply add a >hash-table to make untimeout more effecient, and not lose backwards >compatability with all of the BSD code? I don't see what else the new >code buys us that couldn't be done simply and with less overhead (in >terms of code and new structure overhead)? > >Then, we'd be O(n) for timeout, O(1) for softclock, and O(1) for >untimeout, which would be the same but with complete backwards >compatability. The best of both worlds. :) I don't want to pay O(n) for anything. Perhaps I'm greedy. I can perform upwards of 200 (real life, seek bound) transactions a second with bonnie on a single Atlas II with the CAM code. I can perform even more if I'm doing sequential reads. I can pretty much sustain that rate to multiple drives meaning even a higher rate of timeout/ untimeout calls. Going from 2 * O(n) to O(n) is not anywhere near the same as going to 2 * O(1). Even in the high resolution timer case, the overhead is still much smaller: O(hash chain) + O(1) ~= 2 * O(1) >Nate -- Justin T. Gibbs =========================================== FreeBSD: Turning PCs into workstations ===========================================
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