On Tue, Feb 19, 2002 at 10:00:04AM -0800, Alfred Perlstein wrote: > * Dominic Marks <[EMAIL PROTECTED]> [020219 09:53] wrote: > > Hey, > > > > On Tue, Feb 19, 2002 at 09:19:56AM -0800, Kip Macy wrote: > > > > Apache will switch to this method at some point. I really can't > > > > understand why they went with that complicated pre-forking stuff. > > > > Using non-blockijng I/O is just not that hard." > > > > > > As mentioned previously, due to the blocking semantics of file I/O on unix, > > > single process servers will only provide peak throughput if everything is > > > resident. By pre-forking, data can continued to be served if one process blocks > > > on file I/O. Apache already handles multiple connections within a process, so > > > it does something like this already. > > > > Yes.. but if your using non-blocking IO for both the disc and network > > read/writes, this no longer applies. If I understand correctly in > > normal operation a server like tHttpd simply blocks on kevent() and > > when a descriptor becomes available for servicing it handles this > > occurance, or occurances since a single kevent() call can return more > > than a single event and then goes back to blocking. Reads and writes > > don't block if they don't complete, you simply get another event when > > the descriptor becomes available again. > > > > Am I wrong? > > Yes, you are wrong. > > Disk IO can't be done in a non-blocking manner. If the kernel doesn't > have the portion of the file you wish to read in the buffer cache > then the process will block waiting. There is simply nothing you > can do about this other than to offload that blocking into another > process context via kernel threads, posix aio or kses. >
Thanks for the lesson! > -- > -Alfred Perlstein [[EMAIL PROTECTED]] > 'Instead of asking why a piece of software is using "1970s technology," > start asking why software is ignoring 30 years of accumulated wisdom.' > Tax deductible donations for FreeBSD: http://www.freebsdfoundation.org/ -- Dominic To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
