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SubjectRe: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift
On Fri, Nov 19, 2010 at 12:56:50AM +0300, Cyrill Gorcunov wrote:
...
> ---
> arch/x86/kernel/cpu/perf_event_p4.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> =====================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
> +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> @@ -753,19 +753,22 @@ out:
>
> static inline int p4_pmu_clear_cccr_ovf(struct hw_perf_event *hwc)
> {
> - int overflow = 0;
> - u32 low, high;
> + u32 overflow = 0;
> + u32 low, low_cccr, high;
>
> - rdmsr(hwc->config_base + hwc->idx, low, high);
> + /* an official way for overflow indication */
> + rdmsr(hwc->config_base + hwc->idx, low_cccr, high);
> + overflow |= (low_cccr & P4_CCCR_OVF);
> +
> + /* unflagged overflows */
> + rdmsr(hwc->event_base + hwc->idx, low, high);
> + overflow |= high & 0x80000000;
>
> - /* we need to check high bit for unflagged overflows */
> - if ((low & P4_CCCR_OVF) || !(high & (1 << 31))) {
> - overflow = 1;
> + if (overflow)

this should be rather 'if (low_cccr & P4_CCCR_OVF)' otherwise
redundant checking_wrmsrl called, updated patch below

/me seems should not touch code at all today
---

perf, x86: P4 PMU - Fix unflagged overflows handling

Jason pointed out that kgdb no longer works with new
nmi-watchdog. Don found the reason -- P4 PMU reads CCCR
register instead of counter itself, it forces NMIs to
be eaten by perf subsystem.

Fix it by reading a proper register.

v2: Call checking_wrmsrl only if needed

Reported-by: Jason Wessel <jason.wessel@windriver.com>
Reported-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---

Jason I've removed your Tested-by because the patch differ a bit

arch/x86/kernel/cpu/perf_event_p4.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
+++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
@@ -753,19 +753,23 @@ out:

static inline int p4_pmu_clear_cccr_ovf(struct hw_perf_event *hwc)
{
- int overflow = 0;
- u32 low, high;
+ u32 overflow = 0;
+ u32 low_cntr, low_cccr, high;

- rdmsr(hwc->config_base + hwc->idx, low, high);
+ /* an official way for overflow indication */
+ rdmsr(hwc->config_base + hwc->idx, low_cccr, high);
+ overflow |= (low_cccr & P4_CCCR_OVF);

- /* we need to check high bit for unflagged overflows */
- if ((low & P4_CCCR_OVF) || !(high & (1 << 31))) {
- overflow = 1;
+ if (overflow) {
(void)checking_wrmsrl(hwc->config_base + hwc->idx,
- ((u64)low) & ~P4_CCCR_OVF);
+ ((u64)low_cccr) & ~P4_CCCR_OVF);
}

- return overflow;
+ /* unflagged overflows */
+ rdmsr(hwc->event_base + hwc->idx, low_cntr, high);
+ overflow |= high & 0x80000000;
+
+ return overflow > 0;
}

static void p4_pmu_disable_pebs(void)

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