Re: [RESEND PATCH v4 00/11] perf/cxlpmu: Misc sashiko raised issues fixes

[Dave Jiang <dave.jiang@intel.com>]

On 9/15/26 3:43 PM, Ian Rogers wrote:
> On Wed, Aug 5, 2026 at 9:02 AM Dave Jiang <dave.jiang@intel.com> wrote:
>>
>> [resend, mangled linux-cxl mailing addr]
>>
>> Teed off of Davidlohr's misc cxlpmu series [1]. I had Claude pick up all
>> the sashiko raised issues and then continued multiple internal review
>> iterations to pick up a number of fixes. I'm no CXL PMU or perf expert,
>> but the fixes look reasonable to me AFAICT.
>>
>> Since v3:
>> - 4/11 and 5/11 swapped, so the one-line MSI vector 0 fix comes before the
>>   info->msi_vec rename and backports on its own (Robin).
>> - 6/11: new patch, add the PMUs after configuring events.
>> - 7/11: no code change; the commit message no longer overstates what
>>   dropping IRQF_SHARED costs a device that shares a vector.
>> - 8/11: quote the spec sentence that makes the freeze sticky, and correct
>>   the claim about what the migration window leaves enabled (Richard,
>>   sashiko-bot).
>> - 10/11: split the probe-time overflow clear out, so this is back to the
>>   single hunk Jonathan acked.
>> - 11/11: new patch. Clear a counter's stale overflow status when starting
>>   an event, which is where the reuse case bites; the probe clear moved
>>   here from 10/11 (Richard).
>>
>> Since v2:
>> - 1/11: check event_idx alongside counter_idx (Jonathan).
>> - 2/11: use FIELD_MODIFY() rather than mask-then-OR (Jonathan).
>> - 3/11: rewrite the rationale, no code change (Jonathan).
>> - 5/11: new patch, split the MSI vector out of info->irq (Robin, Jonathan).
>> - 7/11: drop IRQF_SHARED as well as adding IRQF_NOBALANCING, and retitle
>>   (Jonathan, Robin).
>> - 8/11: don't unfreeze if the PMU has been disabled meanwhile (Robin,
>>   Jonathan).
>> - 10/11: retitle, and drop the cxl_pmu_offline_cpu() hunk since that
>>   dev_err() cannot be reached (Robin).
>> - Dropped the old 9/9 that guarded cpumask_show() against cpumask_of(-1).
>>   The init case was a false positive and neither reviewer liked the shape
>>   of it (Jonathan, Robin).
>>
>> Since v1:
>> - Updated 3/9 to address sashiko issue.
>> - No other changes as sashiko only raised issue with pre-existing.
>>
>> Three follow-ups this series does not attempt:
>>
>> cxl_pmu_read() relies on local64_t being same-CPU, which is the only reason
>> the interrupt has to be pinned at all. Moving prev_count and event->count
>> off local64_t would make the affinity question moot, and Robin may have a
>> view on whether that is worth doing.
>>
>> cxl_pmu_offline_cpu() still leaves on_cpu at -1 across a sleeping
>> perf_pmu_migrate_context(), and still has an unreachable no-target branch.
>> Both want removing, possibly on top of the generic PMU hotplug rework
>> Jonathan pointed at [2].
>>
>> Firmware can leave a counter enabled with Global Freeze on Overflow but not
>> Interrupt on Overflow, which stalls the whole CPMU with no interrupt to say
>> so. Quiescing the block at probe needs two writes per counter to stay
>> within the spec's rule about changing an enabled counter, so it belongs in
>> its own patch.
>>
>> [1]: https://lore.kernel.org/linux-cxl/20260715191454.459673-1-dave@stgolabs.net/
>> [2]: https://lore.kernel.org/linux-arm-kernel/cover.1784911757.git.robin.murphy@arm.com/
> 
> 
> Thanks Dave, I notice that everything seems ready to land for this
> series. Is there anything pending? Sashiko mentioned pre-existing
> issues.

Hi Ian. Nothing is pending. Don't plan to address the pre-existing issues in the current series. Will look at follow-ups once this series is picked up. Thanks!

> 
> Thanks,
> Ian
> 
>> Dave Jiang (11):
>>   perf/cxl: Program the requested event group on configurable counters
>>   perf/cxl: Clear stale event fields before reprogramming a counter
>>   perf/cxl: Fix the counter overflow delta fixup
>>   perf/cxl: Accept an overflow interrupt on MSI message number 0
>>   perf/cxl: Split the MSI vector out of info->irq
>>   cxl/pci: Add the PMUs after configuring events
>>   perf/cxl: Don't share the overflow interrupt, and keep it pinned
>>   perf/cxl: Unfreeze counters after handling an overflow interrupt
>>   perf/cxl: Validate the hardware-reported counter width
>>   perf/cxl: Don't log through pmu.dev in the overflow interrupt handler
>>   perf/cxl: Clear stale overflow status before using a counter
>>
>>  drivers/cxl/pci.c      |  11 +++--
>>  drivers/perf/cxl_pmu.c | 107 ++++++++++++++++++++++++++++++++---------
>>  2 files changed, 90 insertions(+), 28 deletions(-)
>>
>>
>> base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff
>> --
>> 2.54.0
>>
>>