On Sun, 2009-08-23 at 14:05 +0300, raz ben yehuda wrote: > On Sun, 2009-08-23 at 09:30 +0200, Mike Galbraith wrote: > > On Sun, 2009-08-23 at 12:09 +0300, raz ben yehuda wrote: > > > On Sun, 2009-08-23 at 07:21 +0200, Mike Galbraith wrote: > > > > > > Seems to me this boils down to a different way to make a SW box in a HW > > > > box, which already exists. What does this provide that partitioning a > > > > box with csets and virtualization doesn't? > > > OFFSCHED does not compete with cpu sets nor virtualization.it is > > > different. > > > > > > 1. Neither virtuallization nor cpu sets provide hard real time. OFFSCHED > > > does this with a little cost and no impact on the OS.OFFSCHED is not > > > just accurate , it is also extremely fast,after all, it is NMI'ed > > > processor. > > > > Why not? Why can't I run an RT kernel with an RTOS guest and let it do > > it's deadline management thing? > Have you ever tested how long a single context switch cost ? can you run > this system with a 1us accuracy ? you cannot.try ftrac'ing your system. > the interrupt alone costs several hundreds nano seconds. By the time you > will be reaching your code, the deadline will be nearly gone. I've measured context switch cost many times. The point though, wasn't how tight a constraint may be, you maintained that realtime was out the window, and I didn't see any reason for that to be the case. > > > 2. OFFSCHED has a access to every piece of memory in the system. so it > > > can act as a centry for the system, or use linux facilities. Also, the > > > kernel can access OFFSCHED memory, it is the same address space. > > > > Hm. That appears to be a self negating argument. > correct. but I can receive packets over napi and transmit packets over hard_start_xmit > much faster than any guest OS. I can disable interrupts and move to poll > mode, thus helping the operating system. can a guest OS help linux? Depends entirely on the job at hand. If the job is running a firewall in kernel mode, no it won't cut the mustard. (no offense intended, but this all sounds like a great big kernel module to me, one which doesn't even taint the kernel) > > > 3. OFFSCHED can improve the linux OS ( NAPI,OFFSCHED firewall,RTOP ), > > > while a guest OS cannot. > > > > > > 4. cpu sets cannot replace softirqs and hardirqs. OFFSCHED can. cpu sets > > > deals with kernel threads and user space threads. in OFFSCHED we use > > > offlets. > > > > Which still looks like OS-fu to me. > I do not understand this remark. Whether it's offlet, tasklet, insert buzz-word of the day, it's thread of execution management, which I called OS-fu, ie one of those things that OSs do. The rest, I'll leave off replying to, we're kinda splitting hairs. I don't see a big generic benefit to OFFSCHED or ilk, others do. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
