Re: [PATCH V4 0/1] powerpc/perf: Clear pending PMI in ppmu callbacks
On Wed, 21 Jul 2021 01:48:28 -0400, Athira Rajeev wrote: > Running perf fuzzer testsuite popped up below messages > in the dmesg logs: > > "Can't find PMC that caused IRQ" > > This means a PMU exception happened, but none of the PMC's (Performance > Monitor Counter) were found to be overflown. Perf interrupt handler checks > the PMC's to see which PMC has overflown and if none of the PMCs are > overflown ( counter value not >= 0x8000 ), it throws warning: > "Can't find PMC that caused IRQ". > > [...] Applied to powerpc/next. [1/1] powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting an overflown PMC https://git.kernel.org/powerpc/c/2c9ac51b850d84ee496b0a5d832ce66d411ae552 cheers
Re: [PATCH V4 0/1] powerpc/perf: Clear pending PMI in ppmu callbacks
Excerpts from Athira Rajeev's message of November 20, 2021 12:36 am: > > >> On 21-Jul-2021, at 11:18 AM, Athira Rajeev >> wrote: >> >> Running perf fuzzer testsuite popped up below messages >> in the dmesg logs: >> >> "Can't find PMC that caused IRQ" >> >> This means a PMU exception happened, but none of the PMC's (Performance >> Monitor Counter) were found to be overflown. Perf interrupt handler checks >> the PMC's to see which PMC has overflown and if none of the PMCs are >> overflown ( counter value not >= 0x8000 ), it throws warning: >> "Can't find PMC that caused IRQ". >> >> Powerpc has capability to mask and replay a performance monitoring >> interrupt (PMI). In case of replayed PMI, there are some corner cases >> that clears the PMCs after masking. In such cases, the perf interrupt >> handler will not find the active PMC values that had caused the overflow >> and thus leading to this message. This patchset attempts to fix those >> corner cases. >> >> However there is one more case in PowerNV where these messages are >> emitted during system wide profiling or when a specific CPU is monitored >> for an event. That is, when a counter overflow just before entering idle >> and a PMI gets triggered after wakeup from idle. Since PMCs >> are not saved in the idle path, perf interrupt handler will not >> find overflown counter value and emits the "Can't find PMC" messages. >> This patch documents this race condition in powerpc core-book3s. >> >> Patch fixes the ppmu callbacks to disable pending interrupt before clearing >> the overflown PMC and documents the race condition in idle path. >> >> Changelog: >> changes from v3 -> v4 >> Addressed review comments from Nicholas Piggin >> - Added comment explaining the need to clear MMCR0 PMXE bit in >> pmu disable callback. >> - Added a check to display warning if there is a PMI pending >> bit set in Paca without any overflown PMC. >> - Removed the condition check before clearing pending PMI >> in 'clear_pmi_irq_pending' function. >> - Added reviewed by from Nicholas Piggin. >> >> Changes from v2 -> v3 >> Addressed review comments from Nicholas Piggin >> - Moved the clearing of PMI bit to power_pmu_disable. >> In previous versions, this was done in power_pmu_del, >> power_pmu_stop/enable callbacks before clearing of PMC's. >> - power_pmu_disable is called before any event gets deleted >> or stopped. If more than one event is running in the PMU, >> we may clear the PMI bit for an event which is not going >> to be deleted/stopped. Hence introduced check in >> power_pmu_enable to set back PMI to avoid dropping of valid >> samples in such cases. >> - Disable MMCR0 PMXE bit in pmu disable callback which otherwise >> could trigger PMI when PMU is getting disabled. >> Changes from v1 -> v2 >> Addressed review comments from Nicholas Piggin >> - Moved the PMI pending check and clearing function >> to arch/powerpc/include/asm/hw_irq.h and renamed >> function to "get_clear_pmi_irq_pending" >> - Along with checking for pending PMI bit in Paca, >> look for PMAO bit in MMCR0 register to decide on >> pending PMI interrupt. >> >> Athira Rajeev (1): >> powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting >>an overflown PMC > > Hi, > > Please let me know if there are any review comments for this patch. > > Thanks > Athira It seems good to me. It already has my R-B. Would be good if we can get this one merged. Thanks, Nick
Re: [PATCH V4 0/1] powerpc/perf: Clear pending PMI in ppmu callbacks
> On 21-Jul-2021, at 11:18 AM, Athira Rajeev > wrote: > > Running perf fuzzer testsuite popped up below messages > in the dmesg logs: > > "Can't find PMC that caused IRQ" > > This means a PMU exception happened, but none of the PMC's (Performance > Monitor Counter) were found to be overflown. Perf interrupt handler checks > the PMC's to see which PMC has overflown and if none of the PMCs are > overflown ( counter value not >= 0x8000 ), it throws warning: > "Can't find PMC that caused IRQ". > > Powerpc has capability to mask and replay a performance monitoring > interrupt (PMI). In case of replayed PMI, there are some corner cases > that clears the PMCs after masking. In such cases, the perf interrupt > handler will not find the active PMC values that had caused the overflow > and thus leading to this message. This patchset attempts to fix those > corner cases. > > However there is one more case in PowerNV where these messages are > emitted during system wide profiling or when a specific CPU is monitored > for an event. That is, when a counter overflow just before entering idle > and a PMI gets triggered after wakeup from idle. Since PMCs > are not saved in the idle path, perf interrupt handler will not > find overflown counter value and emits the "Can't find PMC" messages. > This patch documents this race condition in powerpc core-book3s. > > Patch fixes the ppmu callbacks to disable pending interrupt before clearing > the overflown PMC and documents the race condition in idle path. > > Changelog: > changes from v3 -> v4 > Addressed review comments from Nicholas Piggin > - Added comment explaining the need to clear MMCR0 PMXE bit in > pmu disable callback. > - Added a check to display warning if there is a PMI pending > bit set in Paca without any overflown PMC. > - Removed the condition check before clearing pending PMI > in 'clear_pmi_irq_pending' function. > - Added reviewed by from Nicholas Piggin. > > Changes from v2 -> v3 > Addressed review comments from Nicholas Piggin > - Moved the clearing of PMI bit to power_pmu_disable. > In previous versions, this was done in power_pmu_del, > power_pmu_stop/enable callbacks before clearing of PMC's. > - power_pmu_disable is called before any event gets deleted > or stopped. If more than one event is running in the PMU, > we may clear the PMI bit for an event which is not going > to be deleted/stopped. Hence introduced check in > power_pmu_enable to set back PMI to avoid dropping of valid > samples in such cases. > - Disable MMCR0 PMXE bit in pmu disable callback which otherwise > could trigger PMI when PMU is getting disabled. > Changes from v1 -> v2 > Addressed review comments from Nicholas Piggin > - Moved the PMI pending check and clearing function > to arch/powerpc/include/asm/hw_irq.h and renamed > function to "get_clear_pmi_irq_pending" > - Along with checking for pending PMI bit in Paca, > look for PMAO bit in MMCR0 register to decide on > pending PMI interrupt. > > Athira Rajeev (1): > powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting >an overflown PMC Hi, Please let me know if there are any review comments for this patch. Thanks Athira > > arch/powerpc/include/asm/hw_irq.h | 38 + > arch/powerpc/perf/core-book3s.c | 59 ++- > 2 files changed, 96 insertions(+), 1 deletion(-) > > -- > 1.8.3.1 >
[PATCH V4 0/1] powerpc/perf: Clear pending PMI in ppmu callbacks
Running perf fuzzer testsuite popped up below messages in the dmesg logs: "Can't find PMC that caused IRQ" This means a PMU exception happened, but none of the PMC's (Performance Monitor Counter) were found to be overflown. Perf interrupt handler checks the PMC's to see which PMC has overflown and if none of the PMCs are overflown ( counter value not >= 0x8000 ), it throws warning: "Can't find PMC that caused IRQ". Powerpc has capability to mask and replay a performance monitoring interrupt (PMI). In case of replayed PMI, there are some corner cases that clears the PMCs after masking. In such cases, the perf interrupt handler will not find the active PMC values that had caused the overflow and thus leading to this message. This patchset attempts to fix those corner cases. However there is one more case in PowerNV where these messages are emitted during system wide profiling or when a specific CPU is monitored for an event. That is, when a counter overflow just before entering idle and a PMI gets triggered after wakeup from idle. Since PMCs are not saved in the idle path, perf interrupt handler will not find overflown counter value and emits the "Can't find PMC" messages. This patch documents this race condition in powerpc core-book3s. Patch fixes the ppmu callbacks to disable pending interrupt before clearing the overflown PMC and documents the race condition in idle path. Changelog: changes from v3 -> v4 Addressed review comments from Nicholas Piggin - Added comment explaining the need to clear MMCR0 PMXE bit in pmu disable callback. - Added a check to display warning if there is a PMI pending bit set in Paca without any overflown PMC. - Removed the condition check before clearing pending PMI in 'clear_pmi_irq_pending' function. - Added reviewed by from Nicholas Piggin. Changes from v2 -> v3 Addressed review comments from Nicholas Piggin - Moved the clearing of PMI bit to power_pmu_disable. In previous versions, this was done in power_pmu_del, power_pmu_stop/enable callbacks before clearing of PMC's. - power_pmu_disable is called before any event gets deleted or stopped. If more than one event is running in the PMU, we may clear the PMI bit for an event which is not going to be deleted/stopped. Hence introduced check in power_pmu_enable to set back PMI to avoid dropping of valid samples in such cases. - Disable MMCR0 PMXE bit in pmu disable callback which otherwise could trigger PMI when PMU is getting disabled. Changes from v1 -> v2 Addressed review comments from Nicholas Piggin - Moved the PMI pending check and clearing function to arch/powerpc/include/asm/hw_irq.h and renamed function to "get_clear_pmi_irq_pending" - Along with checking for pending PMI bit in Paca, look for PMAO bit in MMCR0 register to decide on pending PMI interrupt. Athira Rajeev (1): powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting an overflown PMC arch/powerpc/include/asm/hw_irq.h | 38 + arch/powerpc/perf/core-book3s.c | 59 ++- 2 files changed, 96 insertions(+), 1 deletion(-) -- 1.8.3.1
