On Tue, Nov 20, 2012 at 04:31:58PM +0000, Robert Richter wrote: > On 20.11.12 15:57:17, Will Deacon wrote: > > On Tue, Nov 20, 2012 at 12:17:47PM +0000, Robert Richter wrote: > > > > > > since this is just an update of cpu detection I would be willing to > > > include this into kernel code anyway. > > > > Perhaps, but one day we might like to remove this compatibility layer as > > tools move over to the perf system call, so adding new CPUs here is actively > > going against that. > > This would help people to use oprofile as they did before with legacy > oprofile tools. There is not much effort to keep oprofile kernel > support for these tools if in-kernel perf_event support exists for new > hardware. As this is not much effort to maintain, we could keep > supporting this. Forcing users to use operf since this is the only > way to connect to newer hardware might not be what they want.
For arch/arm/, yes, it's not a lot of work but I'm thinking more of things like heterogeneous multi-core (big/little) and arm64, which we definitely don't want to deal with in the old tools. I think newer hardware really will require operf. > > > We could further move the cpu detection to userspace if perf_event > > > exists. We let the kernel enable oprofile with cpu_type="unknown". > > > User space then could either bind mount the file (user could do this > > > manually) or we implement to write to cpu_type. Doing so oprofile > > > could use in-kernel perf_events if it exists always as fallback. > > > > Not sure I follow you... operf already does the CPU detection from > > userspace, so I guess that code could simply be re-used. What does the bind > > mount involve? > > I am thinking of the following: > > # cat /root/cpu_type > arm/armv7-ca5 > # cat /dev/oprofile/cpu_type > unknown > # mount --bind /root/cpu_type /dev/oprofile/cpu_type > # cat /dev/oprofile/cpu_type > arm/armv7-ca5 > > From here legacy oprofile tools work as expected using oprofilefs. (I > think. Did not test it.) We need to change the kernel for this a bit > to return 'unknown'. The mount could be done by the oprofile tools > using existing cpu detection code. This is only one way to setup > cpu_type from userland, there could be other ways too. Ok, this is functionally equivalent to the patch that was submitted at the start of this thread: it solves the problem of mapping a single ARM core to a oprofile's CPU ID string. Technically, I don't mind doing that in the kernel (at least, it means you don't need to do your trick above) but going forward it *will* fall apart and people will have to move to newer tools. So the question is: do we want to migrate users now or later? Cheers, Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
