Denis Vlasenko wrote: > On Thursday 11 January 2007 18:13, Michael Tokarev wrote: >> example, which isn't quite possible now from userspace. But as long as >> O_DIRECT actually writes data before returning from write() call (as it >> seems to be the case at least with a normal filesystem on a real block >> device - I don't touch corner cases like nfs here), it's pretty much >> THE ideal solution, at least from the application (developer) standpoint. > > Why do you want to wait while 100 megs of data are being written? > You _have to_ have threaded db code in order to not waste > gobs of CPU time on UP + even with that you eat context switch > penalty anyway.
Usually it's done using aio ;) It's not that simple really. For reads, you have to wait for the data anyway before doing something with it. Omiting reads for now. For writes, it's not that problematic - even 10-15 threads is nothing compared with the I/O (O in this case) itself -- that context switch penalty. > I hope you agree that threaded code is not ideal performance-wise > - async IO is better. O_DIRECT is strictly sync IO. Hmm.. Now I'm confused. For example, oracle uses aio + O_DIRECT. It seems to be working... ;) As an alternative, there are multiple single-threaded db_writer processes. Why do you say O_DIRECT is strictly sync? In either case - I provided some real numbers in this thread before. Yes, O_DIRECT has its problems, even security problems. But the thing is - it is working, and working WAY better - from the performance point of view - than "indirect" I/O, and currently there's no alternative that works as good as O_DIRECT. Thanks. /mjt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
