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

[Jonathan Cameron <jic23@kernel.org>]

On Wed,  5 Aug 2026 08:59:00 -0700
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.

+CC Robert given Robert is talking about what needs adding to this driver at
LPC and so presumably has hardware (and will send lots of nice patches
for this driver shortly ;)

https://lpc.events/event/20/contributions/2521/


> 
> 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/
> 
> 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