Date: Thu, 27 Apr 2000 13:43:41 -0700 From: Jake Burkholder <jburkhol@home.com> To: Doug Rabson <dfr@nlsystems.com> Cc: Jake Burkholder <jburkhol@home.com>, Bruce Evans <bde@zeta.org.au>, Boris Popov <bp@butya.kz>, freebsd-current@FreeBSD.ORG Subject: Re: SMP changes and breaking kld object module compatibility Message-ID: <20000427204341.9648DBCA7@io.yi.org> In-Reply-To: Message from Doug Rabson <dfr@nlsystems.com> of "Tue, 25 Apr 2000 21:50:25 BST." <Pine.BSF.4.21.0004252146030.79607-100000@salmon.nlsystems.com>
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...snip... > > Its nice to see someone actually using kobj so soon. There is a possible > performance problem though - kobj method calls are roughly 20% slower than > direct function calls. Having said that, this isn't that slow - I timed a > method call to a two argument function at ~40ns on a 300MHz PII. > > I could improve this for some applications (including this one) by > providing a mechanism for an application to cache the function pointer > returned by the method lookup. Yes, this sounds interesting. I can see that there are provisions for a cache in the code, and I can see from the sysctls that hits and misses are happening, but I can't see where the function pointers are entered into the cache. Is this enabled by default? It also might be possible to have default implementations that do "less than nothing", a special value could be entered in the cache that indicates don't call through the function pointer at all. I don't know how an inline cache lookup would compare to an empty function call, but it might be a win when the locks are supposed to do nothing. Anyway, I've made a patch that uses Boris's suggestion of providing functions with empty bodies. I worry about optimizing for the static UP kernel because of introducing more SMP and KLD_MODULE ifdefs, possibly it should just be a function call in all cases. http://io.yi.org/lock.diff I will send-pr it if no one has any comments. Jake To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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