On 2007.06.12 08:02:46 -0700, Stephane Eranian wrote: > Hello, > > I am working on perfmon2 to allow Oprofile and perfmon2 to co-exist > as suggested by Andi Kleen. I looked at the Oprofile init/shutdown > code and I am puzzled by several things which you might be able to > explain for me. I am looking at 2.6.22-rc3. > > Here are the issues: > > * model->fill_in_addresses is called once for all CPUs > on X86, it does more than just filling in the addresses, > it also coordinates with the NMI watchdog by reserving > registers via the reserve_*nmi() interface. > > The problem is that the release of the registers is done > in model->shutdown() which happens to be executed on every > CPU. So you end up releasing the registers too many times. > This is *not* harmless once you start sharing the PMU with > other subsystems given the way the allocator is designed.
Hm, currently it should be ok to move the call to model->shutdown() into nmi_shutdown(), but you might want to instead set addr to 0 when the register is released to still allow for per cpu actions in shutdown(). > * allocate_msrs() allocates two tables per CPU. One for the > counters, the other for the eventsel registers. But then > nmi_setup() copies the cpu_msrs[0] into cpu_msrs[] of all > other cpus. This operation overrides the cpu_msrs[].counters > and cpu_msrs[].controls pointers for all CPUs but CPU0. > But free_msrs() will free the same tables multiple times. This > causes a kernel dump when you enable certain kernel debugging > features. The fix is to copy the content of the counters and > controls array, not the pointers. This was fixed in commit 0939c17c7bcf1. > * the fill_in_addresses() callback for X86 invokes the NMI watchdog > reserve_*_nmi() register allocation routines. This is done regardless > of whether the NMI watchdog is active. When the NMI watchdog is not > active, the allocator will satisfy the allocation for the first MSR > of each type (counter or control), but then it will reject any > request for the others. You end up working with a single > counter/control register. Hm, ouch. I'll try to move the reservation parts into a separate system. Björn - 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/
