Re: [PATCH v4 6/6] perf mem record: Use the IBS swfilt filter when available

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Sep 25, 2026 at 09:32:42AM +0530, Ravi Bangoria wrote:
> Hi Arnaldo,
> 
> > IBS events with exclude_{user,kernel} bits, as used for per-thread
> > recording when kernel samples are not allowed, are rejected on hardware
> > without the privilege filter, so per-thread 'perf mem record' fails on
> > AMD:
> > 
> >   $ perf mem record -o /dev/null -- true
> >   Failure to open event 'ibs_op/ldlat=0/u' on PMU 'ibs_op' which will be removed.
> > 
> > Kernel v6.14 added swfilt, a software privilege filter exposed as the
> > 'swfilt' format term, making those events usable per-thread.  Give the
> > ibs_op memory events extra tables with the term, selected in
> > perf_pmu__arch_init() when the PMU exposes it, keeping the names that
> > need system wide mode otherwise; the knowledge that IBS needs this
> > stays in the arch code.
> > 
> > Suggested-by: Namhyung Kim <namhyung@kernel.org>
> > Suggested-by: Ravi Bangoria <ravi.bangoria@amd.com>
> > Assisted-by: LLM
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
> 
> > + * ... Keep it even when
> > + * the event has no exclude bits yet, 'perf record' adds them on the
> > + * first open failure and retries with the same name.
> 
> Currently, 'perf record' fails rather than silently retrying with
> /swfilt=1/. The reason to not transparently add /swfilt=1/ is to
> make the user aware that software filtering is being used, and it
> is not overhead free.

Made it more concise:

+/*
+ * IBS events with exclude_{user,kernel} bits are rejected on hardware
+ * without the privilege filter unless swfilt is used: the extra tables
+ * carry the term, selected when the PMU exposes it.
+ */
 struct perf_mem_event perf_mem_events_amd[PERF_MEM_EVENTS__MAX] = {
        E(NULL,         NULL,           NULL,   false,  0),
        E(NULL,         NULL,           NULL,   false,  0),
        E("mem-ldst",   "%s//",         NULL,   false,  0),
 };

+struct perf_mem_event perf_mem_events_amd_swfilt[PERF_MEM_EVENTS__MAX] = {
+       E(NULL,         NULL,           NULL,   false,  0),
+       E(NULL,         NULL,           NULL,   false,  0),
+       E("mem-ldst",   "%s/swfilt=1/", NULL,   false,  0),
+};
+
 struct perf_mem_event perf_mem_events_amd_ldlat[PERF_MEM_EVENTS__MAX] = {
        E(NULL,         NULL,           NULL,   false,  0),
        E(NULL,         NULL,           NULL,   false,  0),
        E("mem-ldst",   "%s/ldlat=%u/", NULL,   true,   0),
 };
+
+struct perf_mem_event perf_mem_events_amd_ldlat_swfilt[PERF_MEM_EVENTS__MAX] = {
+       E(NULL,         NULL,                   NULL,   false,  0),
+       E(NULL,         NULL,                   NULL,   false,  0),
+       E("mem-ldst",   "%s/ldlat=%u,swfilt=1/",        NULL,   true,   0),
+};o
- Arnaldo