2011/10/27 Mike Galbraith <efault@xxxxxx>: > On Thu, 2011-10-27 at 15:03 -0400, Raphaël Beamonte wrote: > >> Moreover, the use of hwlatdetect seems to confirm that the problem is >> from hardware. > > Yeah, skimmed over your message too quick, thinking nsecs instead of > usecs. Probably SMIs. > > -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 > One way to find out whether the spikes in the latency are due to SMI(System Management Interrupt) is to read the MSR register that keeps the count of SMIs. So, read the MSR in the start of the test program and the end of the test and see whether the count has increased. Unfortunately, it is model-specific-register and I am not sure whether AMD supports it. I don't think all Intel processors support it either. I know that Nehalem based Intel Core-i7 arrandale processor supports counting SMI thru MSR 0x34 and I have not found it documented in any Intel documentation but found in some reference BIOS source. I have tested it with legacy USB interrupts and found it to work. RDMSR is a privilege-0 instruction though. -- 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
