Re: [RFC PATCH v3 0/4] mm/damon: introduce perf event based access check

[SeongJae Park <sj@kernel.org>]

On Sat, 25 Apr 2026 21:33:07 +0900 Akinobu Mita <akinobu.mita@gmail.com> wrote:

> 2026年4月25日(土) 8:31 SeongJae Park <sj@kernel.org>:
> >
> > On Fri, 24 Apr 2026 12:27:07 +0900 Akinobu Mita <akinobu.mita@gmail.com> wrote:
> >
> > > Hello SeongJae,
> > >
> > > 2026年4月23日(木) 13:34 SeongJae Park <sj@kernel.org>:
[...]
> > > My current patch introduces a set of kernel ABIs (.../perf_events/<P>/*),
> > > and if I want to control another field in the perf_event_attr,
> > > I would have to add a new ABI. This would be a significant
> > > maintenance cost.
> > >
> > > Instead, I would like to provide a single bin file where the
> > > perf_event_attr I want to set is written as binary.
> >
> > I'd prefer having single file per parameter, as sysfs is designed for.  It
> > allows keeping the input format simple and therefore easy to maintain and
> > extend.  Of course, we should carefult at adding new parameters, though.
> 
> Another idea from Namhyung Kim [1] is to fix the events
> specified by the CPU architecture being executed.

I think I need to study mroe about perf events :)

> 
> Of course, we would want to control a limited number of
> parameters, such as sample_freq.
> 
> [1] https://lore.kernel.org/damon/aZwLDAxf9eP0lPdD@z2/
> 
> > >
> > > > >
> > > > > - `sample freq`: A higher frequency improves access accuracy, but also
> > > > >   increases overhead.
> > > > > - `sample phys addr`: specify 0 for vaddr and 1 for paddr.
> > > > > - The remaining type, config, config1, and config2 settings can be found
> > > > >   as follows:
> > > >
> > > > The values look bit human-unfriendly.  I wonder if we could use more
> > > > human-friendly values, e.g., 'cpu' for type,
> > > > 'mem_trans_retired.load_latency_gt_1024' for config, etc.  Not necessarily we
> > > > need to fix this right now.  Let's keep discussing.
> > >
> > > I'd like to do it that way. These processes can be handled better
> > > from user space than from within the kernel, so I'd like to achieve
> > > this from damo with the help of the perf tool and library.
> >
> > Does existing perf event ABI also take that approach?  If so, I think that is
> > fine.
> 
> On Intel CPUs, you can read the mem-loads and/or mem-stores
> files as follows to find the value that should be set to
> perf_event_attr:
> 
> $ cat /sys/bus/event_source/devices/cpu/events/mem-loads
> event=0xcd,umask=0x1,ldlat=3
> 
> You can find out which bit field of which member of
> perf_event_attr should be used to set these values from the
> corresponding files in the format directory.
> 
> $ cat /sys/bus/event_source/devices/cpu/format/{event,umask,ldlat}
> config:0-7
> config:8-15
> config1:0-15
> 
> This conversion from symbolic event name to values that should
> be set in perf_event_attr can be done, for example, as shown below,
> so I think it should be implemented using perf in some way.
> 
> import perf
> 
> if __name__ == '__main__':
>     evlist = perf.parse_events("mem-loads")
>     for evsel in evlist:
>         print(f"{evsel}: type={evsel.type} config={evsel.config}")

I definitely need to study mroe about perf event.  I will comment after I learn
some fundamentals.  But I believe this is not a blocker of this work.


Thanks,
SJ