Date: Thu, 27 Dec 2007 18:17:28 -0500 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-arch@FreeBSD.org Cc: Poul-Henning Kamp <phk@phk.freebsd.dk> Subject: Re: New "timeout" api, to replace callout Message-ID: <200712271817.28789.jhb@freebsd.org> In-Reply-To: <15391.1196547545@critter.freebsd.dk> References: <15391.1196547545@critter.freebsd.dk>
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On Saturday 01 December 2007 05:19:05 pm Poul-Henning Kamp wrote: > > Here is my proposed new timeout API for 8.x. > > The primary objective is to make it possible to have multiple timeout > "providers" of possibly different kind, so that we can have per-cpu > or per-net-stack timeout handing. > > A secondary goal, is to shove the anti-race handling in destruction of > timeouts back into the implemenation, rather than force users to spend > 20+ lines doing that. I don't see this anymore. Perhaps you haven't looked at updated drivers recently? Right now it looks like this: foo_attach/create() { mtx_init(&foo->lock, ...); callout_init_mtx(&foo->callout, &foo->lock); } foo_something() { callout_reset(&foo->callout, foo_timer, ...) } /* Called with lock held */ foo_timer() { /* * Doesn't have to check 'is detaching' or any other such crap * anymore. */ } foo_stop() { FOO_LOCK(); callout_stop(&foo->callout); /* foo_timer() will no longer run after this point. */ FOO_UNLOCK(); } foo_detach/destroy() { foo_stop(); /* * This drain ensures softclock() is done frobbing with our mutex * so we can safely destroy it. Also makes sure it has no references * to our callout structure either. */ callout_drain(&foo->callout); mtx_destroy(&foo->lock); } That's not 20 lines. You have to do the reset/stop anyway and those now work intuitively. The only "extra" code is an init routine (which you will need anyway) and a teardown routine (callout_drain()). From what I can tell, you've basically mandated a lock and when you use callout_init_mtx() (or now callout_init_rw()), callout_stop() == timeout_safe() and callout_drain() == timeout_cleanup(). Thus, as far as the MPSAFEty stuff, I think the timeout changes are just reshuffling deck chairs. The other goals (axeing hz) I agree with, but I don't think you've changed anything as far as MPSAFEty is concerned. Also, I'd probably find timeout_stop() more intuitive than timeout_safe() to be honest. Maybe timeout_disarm()? -- John Baldwin
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