Date: Sun, 23 Dec 2001 09:58:42 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: David Greenman <dg@root.com> Cc: Bruce Evans <bde@zeta.org.au>, Matthew Dillon <dillon@apollo.backplane.com>, Mike Silbersack <silby@silby.com>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/dev/sio sio.c Message-ID: <61654.1009097922@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 22 Dec 2001 19:32:31 PST." <20011222193231.D24034@nexus.root.com>
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In message <20011222193231.D24034@nexus.root.com>, David Greenman writes: > It seems to me that these days it is more important to optimize for >reducing overflow due to latency than it is to optimize for reducing >overflow due to interrupt overhead. A trigger that is set near the median >of 8 seems like the most reasonable setting to me when considering modern >hardware. David, Bruce has a very valid point here: If our bad^H^H^Hlousy interrupt latency is not visible to developers, people will not think about it until our entire kernel has become a slow monster. My guess would be that only four people in the project who have ever measured our interrupt latency: Bruce, Louie, Warner and me. The rest of the project doesn't notice lousy interrupt latency until timecounters overflow or serial ports drop characters. And if those are the only indications we have, then we should not hide them with duc[kt]-tape. If our interrupt latency is so bad that we cannot run a serial port as well on a PIII/Athlon 1GHz cpu as we could on a 486/66 a few years back, then the solution is not to make the serial driver more defensive, the solution is to fix the interrupt latency. Bruce has been Mr. sio forever, and for all I can see he still fills that position ably and willingly. Matts commit should be backed out and only go in again with either Bruce's accept or an overriding majority of arch@ behind him. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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