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? > 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. > 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. > 5. cpu sets and virtualization are services provided by the kernel to > the "system".who serves the kernel ? who protects the kernel ? If either one can diddle the others ram, they are in no way isolated or protected, so can't even defend against their own bugs. What protects a hard RT deadline from VM pressure, memory bandwidth consumption etc etc? Looks to me like it's soft RT, because you can't control the external variables. > 6. offlets gives the programmer full control over an entire processor. > no preemption, no interrupts, no quiesce. you know what happens , and > when it happens. If I can route interrupts such that only say network interrupts are delivered to my cset/vm core, and the guest OS is a custom high speed low drag application, I just don't see much difference. > I have this hard real time system several years on my SMP/MC/SMT > machines. It serves me well. The core of OFFSCHED patch was 4 lines. > So,i simply compile a ***entirely regular*** linux bzImage and that's > it. It did not mess with drivers, spinlocks, softirqs ..., OFFSCHED just > directed the cpu_down to my own hard real time piece of code. The rest > of the kernel remained the same. Aaaaanyway, I'm not saying it's not a useful thing to do, just saying I don't see any reason you can't get essentially the same result with what's in the kernel now. -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
