Date: Mon, 27 Aug 2001 14:14:16 -0400 (EDT) From: Robert Watson <rwatson@FreeBSD.ORG> To: Bruce Evans <bde@zeta.org.au> Cc: Julian Elischer <julian@elischer.org>, current@FreeBSD.ORG Subject: Re: KSE kernel comparissons Message-ID: <Pine.NEB.3.96L.1010827140546.42016O-100000@fledge.watson.org> In-Reply-To: <20010827170927.V23439-100000@besplex.bde.org>
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On Mon, 27 Aug 2001, Bruce Evans wrote: > How much faster (or slower) will it be for threaded programs (for > various numbers of CPUs)? I don't see how it can be faster for a single > CPU (interrupt threads in the kernel show that using threads tends to > pessimize both efficiency and latency for a single CPU). Note that we won't be able to see some of the impactmpacted until SMPng is further along, where KSE will pessimize a number of single-thread operations. For example, right now SMPng proc locking relies on certain proc structure entries being changed only by curproc, meaning that locks are held for reading only by other processes. With KSE, we'll need to actually hold real locks when acting on those curproc entries (in particular, reads) which may impose a substantial performance overhead. I would anticipate that a number of the other potential shortcuts in SMPng would be similarly impacted by KSE. However, since SMPng is very much a work in progress right now, that's not something I think we can quantify yet. This general issue does raise a lot of concerns however -- many locking assumptions in SMPng will need to be changed, and the locking will need to be much more thorough before we can move forward. Even pre-SMPng, we've had race issues relating to unexpected sleeps, this will only get more hairy (although architecturally better) with SMPng. I'm worried that throwing KSE into the mix is going to hurt a lot. Robert N M Watson FreeBSD Core Team, TrustedBSD Project robert@fledge.watson.org NAI Labs, Safeport Network Services To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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