Date: Thu, 21 Oct 2004 09:37:07 +0400 (MSD) From: Igor Sysoev <is@rambler-co.ru> To: "Ronald F. Guilmette" <rfg@monkeys.com> Cc: freebsd-net@freebsd.org Subject: Re: aio_connect ? Message-ID: <20041021091935.K17688@is.park.rambler.ru> In-Reply-To: <79296.1098306696@monkeys.com> References: <79296.1098306696@monkeys.com>
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On Wed, 20 Oct 2004, Ronald F. Guilmette wrote: > > and they require too many syscalls. > >E.g, the reading requires > >*) 3 syscalls for ready data: aio_read(), aio_error(), aio_return() > >*) 5 syscalls for non-ready data: aio_read(), aio_error(), > > waiting for notification, then aio_error(), aio_return(), > > or if timeout occuired - aio_cancel(), aio_error(). > > This assumes that one is _not_ using the signaling capabilities of the > aio_*() functions in order to allow the kernel to dynamically signal the > userland program upon completion of a previously scheduled async I/O > operation. If however a programmer were to use _that_ approache to de- > tecting I/O completions, then the number of syscals would be reduced > accordingly. Yes, nginx does not use the AIO signaling capabilities. With signals you do not call the syscall that waits the completion. But the call of the signal handler requires 3 context switches instead of 2 switches in the case of syscall. > However this all misses the point. As I noted earlier in this thread, > efficience _for the machines_ is not always one's highest engineering > design goal. If I have a choice between building a more maintainable, > more adaptable, more modularized program, or instead building a more > machine-efficient program, I personally will almost always choose to > build the clearly, more modularized program as opposed to trying to > squeeze every last machine cycle out of the thing. In fact, that is > why I program almost exclusively in higher level languages, even though > I could almost certainly write assembly code that would almost always be > faster. Machine time is worth something, but my time is worth more. I believe if you want to build a more maintainable, more adaptable, more modularized program then you should avoid two things - the threads and the signals. If you like to use a callback behaviour of the signals you could easy implement it without any signal. Igor Sysoev http://sysoev.ru/en/
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