On Mon, Feb 29, 2016 at 03:39:35PM +0000, Will Deacon wrote: > Hi Jan, > > I've queued this lot on my perf/updates branch, but I just noticed an > oddity whilst dealing with some potential conflicts with the kvm tree. > > On Thu, Feb 18, 2016 at 05:50:13PM +0100, Jan Glauber wrote: > > With the long cycle counter bit (LC) disabled the cycle counter is not > > working on ThunderX SOC (ThunderX only implements Aarch64). > > Also, according to documentation LC == 0 is deprecated. > > > > To keep the code simple the patch does not introduce 64 bit wide counter > > functions. Instead writing the cycle counter always sets the upper > > 32 bits so overflow interrupts are generated as before. > > > > Original patch from Andrew Pinksi <andrew.pin...@caviumnetworks.com> > > > > Signed-off-by: Jan Glauber <jglau...@cavium.com> > > --- > > arch/arm64/kernel/perf_event.c | 21 ++++++++++++++++----- > > 1 file changed, 16 insertions(+), 5 deletions(-) > > > > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c > > index 0ed05f6..c68fa98 100644 > > --- a/arch/arm64/kernel/perf_event.c > > +++ b/arch/arm64/kernel/perf_event.c > > @@ -405,6 +405,7 @@ static const struct attribute_group > > *armv8_pmuv3_attr_groups[] = { > > #define ARMV8_PMCR_D (1 << 3) /* CCNT counts every 64th cpu > > cycle */ > > #define ARMV8_PMCR_X (1 << 4) /* Export to ETM */ > > #define ARMV8_PMCR_DP (1 << 5) /* Disable CCNT if > > non-invasive debug*/ > > +#define ARMV8_PMCR_LC (1 << 6) /* Overflow on 64 bit cycle > > counter */ > > #define ARMV8_PMCR_N_SHIFT 11 /* Number of counters > > supported */ > > #define ARMV8_PMCR_N_MASK 0x1f > > #define ARMV8_PMCR_MASK 0x3f /* Mask for writable bits */ > > You haven't extended this mask to cover the LC bit, so it will be ignored > by armv8pmu_pmcr_write afaict.
This is weird. I've double checked and I missed this mask. Annoying. Nevertheless it works for me without the LC bit set. > How did you test this? I can easily update the mask, but it would be > good to know that it doesn't end up cause a breakage. For testing I used: - perf top and perf record & report - looked at interrupt numbers in /proc/interrupts Without the patch _no_ samples at all are recorded and the interrupt does not occur. With the patch I get samples and see a reasonable number of interrupts. Extending the mask so the LC bit is covered would make sense, I'm going to test this now. Jan > Will