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88c7bcad71
Valid perf event sample period value for IBS PMUs (Fetch and Op both)
is limited to multiple of 0x10. perf_ibs_init() has this check:
if (!event->attr.sample_freq && hwc->sample_period & 0x0f)
return -EINVAL;
But it's broken since hwc->sample_period will always be 0 when
event->attr.sample_freq is 0 (irrespective of event->attr.freq value.)
One option to fix this is to change the condition:
- if (!event->attr.sample_freq && hwc->sample_period & 0x0f)
+ if (!event->attr.freq && hwc->sample_period & 0x0f)
However, that will break all userspace tools which have been using IBS
event with sample_period not multiple of 0x10.
Another option is to remove the condition altogether and mask lower
nibble _silently_, same as what current code is inadvertently doing.
I'm preferring this approach as it keeps the existing behavior.
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/r/20250115054438.1021-3-ravi.bangoria@amd.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.