On Thu, 15 Feb 2007, Evgeniy Polyakov wrote: > On Thu, Feb 15, 2007 at 09:05:13AM -0800, Davide Libenzi > (davidel@xmailserver.org) wrote: > > > > I actually think that building chains of syscalls bring you back to a > > multithreaded solution. Why? Because suddendly the service thread become > > from servicing a syscall (with possible cachehit optimization), to > > servicing a whole session. So the number of service threads needed (locked > > down by a chain) becomes big because requests goes from being short-lived > > syscalls to long-lived chains of them. Think about the trivial web server, > > and think about a chain that does open->fstat->sendhdrs->sendfile after an > > accept. What's the difference with a multithreaded solution that does > > accept->clone and execute the above code in the new thread? Nada, NIL. > > That is more ideological question about micro-thread design at all. > If syslet will be able to perform only one syscall, one will have 4 > threads for above case, not one, so it is even more broken.
Nope, just one thread. Well, two, if you consider the "main" dispatch thread, and the syscall service thread. > So, if Linux moves that way of doing AIO (IMO incorrect, I think that > the correct state machine made not of syscalls, but specially crafted > entries - like populate pages into VFS, send chunk, recv chunk without > blocking and continue on completion and the like), syslets with attached > state machines are the (smallest evil) best choice. But at that point you don't need to have complex atom interfaces, with chains, whips and leather pants :) Just code it in C and submit that to the async engine. The longer is the chain though, the closer you get to a fully multithreaded solution, in terms of service thread consuption. And what do you save WRT a multithreaded solution? Not thread creation/destroy, because that cost is fully amortized inside the chain execution cost (plus a pool would even save that). IMO the plus of a generic async engine is mostly from a kernel code maintainance POV. You don't need anymore to have AIO-aware code paths, that automatically transalte to smaller and more maintainable code. - Davide - 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/
